Scope and advances in the catalytic propargylic substitution reaction

Abstract

Nucleophilic displacement of the propargylic alcohol is one of the sought-after methods in the current scenario. The highly nucleophilic alkyne functional moiety along with its considerably acidic terminal hydrogen atom allows the propargylic unit to play a crucial role in organic synthesis by offering a handle for further synthetic transformations. Until 2000, the most fundamental propargylic substitution reaction was the Nicolas reaction, a multi-step transformation, developed in 1972, which involved cobalt as a stoichiometric promoter. Therefore, the direct catalytic substitution of propargylic alcohols was a highly desirable method for development. The pioneering work on the Ru-catalyzed propargylic substitution reaction in 2000 encouraged many researchers to develop several novel catalytic propargylic substitution reactions, which have made rapid progress since then. The purpose of this review is to emphasise the involvement of diverse types of Lewis acid, transition metal and Brønsted acid catalysts in the propargylic substitution reaction and provide an updated summary of the recent developments in this field. The selected examples presented here are the most significant and relevant ones and we believe that this will help the readers to comprehend the scope of the propargylic substitution reaction with diverse types of catalysts and will envisage the scientific community for the future developments in this field.

Scheme 1. Various synthetic transformations of the alkyne moiety.

Fig. 1. Some bioactive molecules with propargylic subunit.

Scheme 2. Propargylic substitution by Nicolas reaction.

Scheme 3. Stoichiometric propargylic substitution reaction.

Scheme 4. Formation of allene derivative during propargylic substitution reaction.

Scheme 5. Different methods for the synthesis of propargylic alcohol.

Scheme 6. Different methods for the synthesis of propargylic alcohol.

Scheme 7. Synthesis of different heterocyclic building blocks from propargyl unit.

Scheme 8. Synthesis of various heterocycles from propargylamine.

Fig. 2. Frequently used elements as catalysts for catalytic propargylic substitution reaction in the periodic table.

Scheme 9. Propargylic substitution reaction via propargylic carbocation intermediate.

Scheme 10. Allylation of propargylic alcohol derivatives with B(C₆F₅)₃.

Scheme 11. Regioselective allylation of propargyl alcohols with BCl₃.

Scheme 12. BF₃·Et₂O catalyzed propargylic substitution and synthesis of δ-lactone thereof.

Scheme 13. Mechanism for the formation of δ-lactam involving propargylic substitution as the key step using BF₃·Et₂O as the catalyst.

Scheme 14. BF₃·Et₂O catalyzed propargylation and the synthesis of substituted 2,5-dialkylthiocyclopentadienes thereof.

Scheme 15. Mechanism of the propargylation of propargylic alcohols catalyzed by BF₃·Et₂O.

Scheme 16. BF₃·Et₂O catalyzed synthesis of substituted indene/furanone from propargyl alcohols.

Scheme 17. Mechanism for the indene formation catalyzed by BF₃·Et₂O.

Scheme 18. BF₃·Et₂O catalyzed synthesis of functionalized dihydroazepines from propargyl alcohols.

Scheme 19. BF₃·Et₂O catalyzed synthesis of quinoline derivatives from propargyl alcohol.

Scheme 20. BF₃·Et₂O catalyzed synthesis of cyclopropylboronic acid pinacol esters from propargyl silyl ethers.

Scheme 21. Mechanism for the BF₃·Et₂O mediated synthesis of synthesis of cyclopropylboronic.

Scheme 22. BF₃·Et₂O catalyzed synthesis of highly-substituted indole-3-carbinols from propargylic alcohols.

Scheme 23. Mechanism for the BF₃·Et₂O mediated synthesis of substituted indole-3-carbinols.

Scheme 24. Al(OTf)₃ catalyzed propargylation of indoles.

Scheme 25. Calcium-catalyzed direct substitution of π-activated alcohols with allyltrimethylsilane.

Scheme 26. Calcium triflate catalyst synthesis of 2H-chromene from propargylic alcohols.

Scheme 27. Mechanism for the Ca-catalyzed synthesis of 2H-chromenes form propargylic alcohols.

Scheme 28. Sc(OTf)₃ catalyzed propargylation of indoles.

Scheme 29. Scandium catalyzed propargylic substitution reaction.

Scheme 30. TiCl₄ catalyzed propargylic substitution with diverse oxygen-centered nucleophiles.

Scheme 31. FeCl₃-catalyzed propargylic substitution reaction of propargylic alcohols.

Scheme 32. FeCl₃ catalyzed propargylic substitution reaction of electron-rich aromatics.

Scheme 33. Propargylic substitution of indoles with FeCl₃ catalyst.

Scheme 34. FeCl₃ catalyzed synthesis of γ-alkynyl ketones from propargylic acetates with enoxysilanes.

Scheme 35. Synthesis of highly conjugated indenes by iron(iii) chloride-catalyzed dimerization of trisubstituted propargylic alcohols.

Scheme 36. Mechanism for the formation of highly conjugated indenes by iron(iii) chloride-catalyzed dimerization of trisubstituted propargylic alcohols.

Scheme 37. FeCl₃ catalyzed intermolecular Friedel–Crafts cyclizations of aryloxy and arylamino-substituted propargylic alcohols.

Scheme 38. Mechanism of FeCl₃ catalyzed synthesis of dihydrobenzofurans and dihydroindoles from propargylic alcohols.

Scheme 39. Ferrocenium hexafluorophosphate ([FeCp₂]PF₆) catalyzed etherification of the terminal, tertiary propargylic alcohols.

Scheme 40. Iron-catalyzed domino reaction of N-cyclohexyl propargyl amines and 1,3-diketones.

Scheme 41. Mechanism of the Fe(iii)-catalyzed propargylation of propargyl amines.

Scheme 42. FeCl₃ catalyzed indene-based polycyclic compounds.

Scheme 43. A proposed mechanism for the FeCl₃-catalyzed synthesis of indenes.

Scheme 44. The nickel catalyzed propargylic substitution reaction.

Scheme 45. Nickel catalyzed enantioselective propargylic substitution reaction.

Scheme 46. Nickel catalyzed substitution of propargyl bromides with deactivated alkyl zinc compounds.

Fig. 3. Conventional ligands used in the nickel catalyzed reaction.

Scheme 47. Ni(i/ii) catalytic cycle for the nickel catalyzed substitution of propargyl bromides with alkylzinc compounds.

Scheme 48. General mechanism for the copper-catalyzed propargylic substitution reaction.

Scheme 49. Allylation of propargylic alcohols catalyzed by Cu(BF₄)₂ catalyst.

Scheme 50. Propargylic amination of various propargylic acetates.

Scheme 51. Mechanism for the propargylic amination of propargyl alcohols.

Scheme 52. Copper-catalyzed enantioselective propargylic amination of propargylic esters.

Fig. 4. Probable transition state for the copper-catalyzed propargylic substitution reaction.

Scheme 53. Copper catalyzed propargylic amination of propargyl esters.

Scheme 54. Cu(OTf)₂ catalyzed synthesis of 2,4,6-trisubstituted pyrimidines from propargylic alcohols.

Scheme 55. Mechanism for the Cu(OTf)₂ catalyzed synthesis of 2,4,6-trisubstituted pyrimidines from propargylic alcohols.

Scheme 56. Propargylic substitution employing cooperative catalysis.

Scheme 57. Mechanism for the propargylation of aldehydes by cooperative catalysis.

Scheme 58. Copper-catalyzed decarboxylative propargylic alkylation of propargyl β-ketoesters.

Scheme 59. Mechanism for the copper-catalyzed decarboxylative propargylic alkylation of propargyl β-ketoesters.

Scheme 60. Enantioselective synthesis of highly functionalized dihydrofurans from propargyl acetates and β-ketoesters.

Scheme 61. Mechanism for the synthesis of highly functionalized dihydrofurans from propargyl acetates and β-ketoesters.

Scheme 62. Copper catalyzed propargylic alkylation of enamines derived from acyclic ketones with propargylic esters.

Fig. 5. Proposed transition state for the Cu-catalyzed substitution of propargylic esters with enamines.

Scheme 63. Cu-catalyzed [3 + 3] cycloaddition of propargylic acetates with cyclic N,N-diethyl-1-enamines.

Scheme 64. Copper catalyzed propargylic amination of propargyl carbamates.

Scheme 65. Cu-catalyzed [3 + 2] cycloaddition of propargylic acetates with monosubstituted hydrazines.

Scheme 66. Competitive pathway for the Cu-catalyzed [3 + 2] cycloaddition of propargylic acetates with monosubstituted hydrazines.

Fig. 6. Proposed transition state for the Cu-catalyzed [3 + 2] cycloaddition of propargylic acetates with monosubstituted hydrazines showing favoured and disfavoured cycloaddition pathway.

Scheme 67. Cu-catalyzed [3 + 2] cycloaddition of propargylic esters with β-enamino esters.

Scheme 68. Plausible mechanism for the Cu-catalyzed [3 + 2] cycloaddition of propargylic esters with β-enamino esters.

Scheme 69. Enantioselective propargylic etherification of propargylic esters with aliphatic alcohols.

Scheme 70. Enantioselective propargylation of trialkyl methantricarboxylate with propargylic alcohol derivatives.

Scheme 71. Synthesis of 2,3-disubstituted indole derivatives from propargylic acetates and anilines using a copper catalyst.

Scheme 72. Mechanism for the synthesis of 2,3-disubstituted indole derivatives from propargylic acetates and anilines using cooperative catalysis.

Scheme 73. Copper-catalyzed [3 + 2] cycloaddition of 3-trimethyl-silylpropargylic acetates with either β-naphthols or electron rich phenols.

Scheme 74. Mechanism for the copper-catalyzed formal [3 + 2] cycloaddition of 3-trimethyl-silylpropargylic acetates with either β-naphthols.

Fig. 7. Probable transition state structure for the copper-catalyzed enantioselective synthesis of benzofurans.

Scheme 75. Copper catalyzed synthesis of chiral phosphonylated 2,3-dihydrofurans.

Scheme 76. Copper-catalyzed asymmetric synthesis of 2,3,4-trisubstituted 2H-1,4-benzoxazines via formal [4 + 2] cycloaddition reaction.

Scheme 77. Highly enantioselective copper-catalyzed propargylic etherification of both aliphatic and aromatic propargylic esters with phenols.

Fig. 8. Probable transition state for the copper-catalyzed enantioselective propargylic etherification reaction.

Scheme 78. Copper catalyzed propargylation of indoles, coumarin derivatives, and enamines.

Fig. 9. Structures of P,N,N ligand and propargylated indoles with corresponding yield and enantioselectivities.

Fig. 10. Structures of propargylated coumarins with corresponding yields and enantioselectivities.

Fig. 11. Structures of propargylated enamines with corresponding yields and enantioselectivities.

Scheme 79. Copper catalyzed substitution reaction of propargyl acetates with P(O)H compounds.

Scheme 80. Mechanism for the novel Cu-catalysed substitution reaction of propargyl acetates with P(O)H compounds.

Scheme 81. Copper-catalyzed enantioselective propargylation of indoles with propargylic esters.

Fig. 12. Structures of different ligands and additives screened in the copper-catalyzed enantioselective propargylation of indoles with propargylic esters.

Scheme 82. Cu-catalyzed direct coupling of the unprotected terminal and internal propargylic alcohols with P(O)H compounds.

Scheme 83. Enantioselective Cu-catalyzed rearrangement of electron-deficient 2-propargyloxy-pyridines.

Fig. 13. Structures of the ligands used for the copper-catalyzed propargylic substitution reaction.

Scheme 84. Mechanism for the enantioselective Cu-catalyzed rearrangement of electron-deficient 2-propargyloxy-pyridines.

Scheme 85. Propargylic dearomatization of phenols.

Fig. 14. Probable transition state structure for the copper-catalyzed Propargylic dearomatization of phenols.

Scheme 86. Decarboxylative [4 + 2] annulation of 4-ethynyl dihydrobenzooxazinones and carboxylic acids via cooperative catalysis.

Scheme 87. Copper catalyzed propargylic etherification reaction.

Fig. 15. Structures of the different borinic acid used.

Fig. 16. Transition state structure for the copper-catalyzed propargylic etherification reaction.

Scheme 88. Direct substitution of propargylic alcohol with oxygen, nitrogen, and carbon nucleophiles catalyzed by molybdenum.

Scheme 89. Molybdenum(vi) catalyzed direct substitution of propargylic alcohols.

Scheme 90. General mechanism for the ruthenium catalyzed propargylic substitution reaction.

Scheme 91. Ruthenium catalyzed propargylic substitution reaction.

Scheme 92. Mechanism for the ruthenium catalyzed propargylic substitution reaction.

Scheme 93. Cationic diruthenium complex catalyzed propargylic thio-etherification reaction.

Scheme 94. Co₂(CO)₈ catalyzed propargylic substitution reaction of deactivated alkenes.

Scheme 95. Ruthenium-catalyzed inter- and intramolecular carbon–carbon bond forming reactions between propargylic alcohols and alkenes.

Scheme 96. Mechanism for the ruthenium catalyzed the synthesis of fused polycyclic compounds.

Scheme 97. Ruthenium- and platinum-catalyzed sequential reactions towards the synthesis of substituted furans from propargylic alcohols and ketones.

Scheme 98. The mechanism for the ruthenium- and platinum-catalyzed sequential reactions towards the synthesis of substituted furans from propargylic alcohols and ketones.

Scheme 99. Ruthenium catalyzed enantioselective propargylic alkylation of propargylic alcohols with acetone.

Scheme 100. Ruthenium catalyzed propargylic substitution reaction of ketones and arynes.

Scheme 101. Ruthenium and gold catalyzed synthesis of substituted oxazoles from propargyl alcohols with terminal alkyne moiety with amides.

Scheme 102. Ruthenium(ii)-catalysed direct propargylation of furan and arene with propargyl alcohols.

Scheme 103. Mechanism for the ruthenium(ii)-catalysed direct propargylation reaction.

Scheme 104. Ruthenium catalyzed propargylic substitution reaction with diverse nucleophiles.

Scheme 105. Mechanism for the ruthenium catalyzed propargylic substitution reaction.

Scheme 106. Ruthenium-catalyzed propargylic reduction of propargylic alcohols with triethylsilane.

Fig. 17. Proposed reactive intermediate for the propargylic reduction with triethysilane.

Scheme 107. Ru-catalyzed propargylic substitution with different nucleophiles.

Scheme 108. Intramolecular cyclization of propargylic alcohols towards the synthesis of chiral chromanes, thiochromanes, and 1,2,3,4-tetrahydroquinolines.

Scheme 109. Probable mechanistic pathway and transition state structure for the ruthenium catalyzed intramolecular cyclization of propargylic alcohols bearing an alkene moiety.

Scheme 110. Ruthenium-catalyzed enantioselective cyclization of propargylic alcohols bearing a thiophene.

Scheme 111. Mechanistic pathway for the ruthenium-catalyzed enantioselective cyclization of propargylic alcohols bearing a thiophene.

Scheme 112. Ruthenium-catalyzed oxypropargylation of alkenes with propargylic alcohols.

Scheme 113. Mechanism for the ruthenium-catalyzed oxypropargylation of alkenes with propargylic alcohols.

Scheme 114. Ruthenium-catalyzed enantioselective synthesis of naphthopyrans by [3 + 3] cycloaddition of propargylic alcohols with 2-naphthols.

Scheme 115. Ruthenium catalyzed enantioselective alpha-propargylation of aldehydes (Path A) and gamma-propargylation of α,β-unsaturated aldehydes (Path B) by cooperative catalysis.

Fig. 18. (a) The key step for the α-propargylation of aldehydes with propargyl alcohols (Path A); (b) the key step for the gamma propargylation of α,β-unsaturated aldehydes with propargylic alcohols (Path B).

Scheme 116. Ruthenium and copper-catalyzed enantioselective propargylic alkylation of propargylic alcohols with β-keto phosphonates.

Scheme 117. Mechanistic pathway for the ruthenium and copper-catalyzed enantioselective propargylic alkylation of propargylic alcohols with β-keto phosphonates.

Scheme 118. Ruthenium and copper-catalyzed enantioselective propargylic alkylation of propargylic alcohols with β-ketoesters.

Scheme 119. Ruthenium-catalyzed [3 + 2] cycloaddition of ethynylcyclopropanes.

Scheme 120. Mechanism for the ruthenium-catalyzed [3 + 2] cycloaddition of ethynylcyclopropanes.

Scheme 121. Highly diastereo- and enantioselective propargylic alkylation of propargylic alcohols with E-enecarbamates.

Fig. 19. Probable transition state structure for the highly diastereo and enantioselective propargylic alkylation of propargylic alcohols with E-ene-carbamates.

Scheme 122. General mechanistic pathway for the rhodium catalyzed propargylic substitution reaction.

Scheme 123. Rhodium-catalyzed propargylic amination of propargylic carbonates.

Scheme 124. Palladium catalyzed enantioselective propargylic amination reaction.

Scheme 125. Palladium-catalyzed synthesis of allenylphosphonates from propargylic derivatives.

Scheme 126. Catalytic cycle for the palladium-catalyzed synthesis of allenyl phosphonates from propargylic derivatives.

Scheme 127. Palladium-catalyzed reaction of propargylic carbonates with Meldrum's acid derivatives.

Scheme 128. Mechanistic pathway for the palladium-catalyzed reaction of propargylic carbonates with Meldrum's acid derivatives.

Scheme 129. Palladium catalyzedregioselective substitution of diaryl acetonitrile to propargylic carbonates.

Scheme 130. Mechanistic pathway for the palladium-catalyzed regioselective substitution of diaryl acetonitrile to propargylic carbonates.

Scheme 131. General mechanism for the silver catalyzed propargylic substitution reaction.

Scheme 132. AgOTf-catalyzed chemoselective approach to 3,5/1,3-disubstituted pyrazoles from propargylic alcohols.

Scheme 133. Mechanism for the AgOTf-catalyzed synthesis of 3,5/1,3-disubstituted pyrazoles from propargylic alcohols.

Scheme 134. Silver(i) catalyzed propargylation of pyrazole with propargyl acetates.

Scheme 135. Probable mechanistic pathway for the silver(i) catalyzed propargylation of pyrazole with propargyl acetates.

Scheme 136. Silver catalyzed synthesis of synthesis of allenylphosphoryl compounds from propargylic alcohol.

Scheme 137. Silver catalyzed synthesis of allenyl-phosphoryl compounds from propargylic alcohols.

Scheme 138. General mechanism for the indium catalyzed propargylic substitution reaction.

Scheme 139. InBr₃ catalyzed C3-propargylation of indoles.

Scheme 140. InBr₃ catalyzed C3-propargylation of indoles.

Scheme 141. In(OTf)₃ catalyzed the stereoselective addition of aldehydes to propargylic alcohols.

Fig. 20. Different organocatalysts screened.

Fig. 21. Probable transition state for the stereoselective addition of aldehydes to propargylic alcohols.

Scheme 142. Enantioselective propargylic alkylation of propargylic alcohols with aldehydes in the presence of InBr₃ and an optically active secondary amine.

Scheme 143. Tin(ii) chloride as an efficient catalyst for the propargylic substitution of secondary propargylic alcohols.

Scheme 144. Mechanistic pathway for the SnCl₂ catalyzed propargylic substitution of propargylic alcohols.

Scheme 145. Synthesis of 1,5-ene-yne using catalytic amounts of SnCl₄ and ZnCl₂.

Scheme 146. Iodine mediated propargylic substitution reaction.

Scheme 147. Iodine mediated propargylic substitution reaction.

Scheme 148. Iodine mediated propargylic substitution reaction.

Scheme 149. PIFA catalyzed propargylic substitution reaction.

Scheme 150. Mechanism for the hypervalent iodine mediated propargylic substitution reaction.

Scheme 151. Iodine mediated reaction of propargyl alcohols and isatin hydrazones for the synthesis of azines.

Scheme 152. Mechanism for the iodine mediated synthesis of azines from propargyl alcohols and isatin hydrazones.

Scheme 153. CeCl₃ catalyzed propargylic substitution reaction.

Scheme 154. Ce(OTf)₃ catalyzed propargylic substitution reaction.

Scheme 155. Mechanism for the Re-catalyzed etherification of propargylic alcohols.

Scheme 156. Re-catalyzed propargylic substitution with allyl trimethyl silane.

Scheme 157. Rhenium catalyzed propargylic substitution reaction.

Scheme 158. Rhenium-and gold-catalyzed synthesis of diethynylmethanes by reactions of propargylic alcohols with trimethyl(phenylethynyl)silane.

Scheme 159. Rhenium catalyzed propargylic substitution reaction.

Scheme 160. Synthesis of various π-activated amines from propargylic alcohols.

Scheme 161. Yb(OTf)₃ catalyzed propargylic substitution of 1,3-dicarbonyls and 4-hydroxycoumarin.

Scheme 162. Yb-catalyzed synthesis of 3-phenyl-1H-indenes form propargyl alcohols.

Scheme 163. Mechanism for the synthesis of 3-phenyl-1H-indenes form propargyl alcohols promoted by Yb-catalyst.

Scheme 164. Yb(OTf)₃ catalyzed efficient method for the synthesis of di- and trisubstituted 2-aryloxazoles from propargylic alcohols.

Scheme 165. Mechanism for the Yb(OTf)₃ catalyzed synthesis of di- and trisubstituted 2-aryloxazoles from propargylic alcohols.

Scheme 166. Iridium catalyzed propargylic substitution with enoxysilane.

Scheme 167. General mechanism for the platinum catalyzed propargylic substitution reaction.

Scheme 168. Pt-catalyzed synthesis of tetrahydrofurans from a propargylic ester by an intramolecular substitution reaction.

Scheme 169. Pt-catalyzed synthesis of cis-2,6-disubstituted morpholines.

Fig. 22. Representative examples of disubstituted-1,4-dioxanes, 3-substituted morpholines, and cyclic sulfamates.

Scheme 170. Proposed mechanism for the intramolecular cyclization.

Scheme 171. Pt(ii)-catalyzed synthesis of phenanthrenes from propargylic alcohols.

Scheme 172. Mechanism of the Pt-catalyzed synthesis of phenanthrenes from propargylic alcohols.

Scheme 173. Gold-catalyzed propargylic substitution reaction.

Scheme 174. Au-catalyzed allylation of propargylic alcohols.

Scheme 175. Mechanism of the gold-catalyzed propargylic substitution reaction.

Scheme 176. Au-catalyzed propargylation of electron rich arenes.

Scheme 177. Au-catalyzed propargylic substitution reactions.

Scheme 178. Gold(iii)-catalyzed regioselective nucleophilic substitution reaction.

Scheme 179. Facile synthesis of 2-substituted piperidines from propargylic alcohols.

Scheme 180. Facile synthesis of two types of 2-substituted piperidines from propargylic alcohols using hard and soft gold catalysts.

Scheme 181. Mechanism for the synthesis of two types of 2-substituted piperidines from propargylic alcohols using hard and soft gold catalysts.

Scheme 182. BiCl₃ catalyzed nucleophilic substitution of propargylic alcohols.

Scheme 183. Bi(OTf)₃ in [BMIM][BF₄] as an efficient catalytic system for allylation, alkynylation, and deoxygenation of propargylic alcohols.

Scheme 184. Bi-catalyzed synthesis of 2-alkenyl furans from propargylic alcohols.

Scheme 185. Mechanism for the Bi-catalyzed synthesis of 2-alkenyl furans from propargylic alcohols.

Scheme 186. General mechanism for the Brønsted acid catalyzed propargylic substitution reaction.

Scheme 187. p-TSA catalyzed propargylic substitution by a heteroatom and carbon-centered nucleophiles.

Scheme 188. p-TSA catalyzed preparation of 1,5-enynes from propargylic alcohols.

Scheme 189. p-TSA catalyzed synthesis of bicyclo[3.1.0]hexanes.

Scheme 190. Nucleophilic substitution of propargylic alcohols catalyzed by p-TSA.

Scheme 191. Synthesis of highly conjugated cyclopenta[c]quinolines from propargylic alcohols catalyzed by p-TSA.

Scheme 192. Mechanistic pathway for the p-TSA/Cu(OTf)₂ catalyzed synthesis of highly conjugated cyclopenta[c]quinolines from propargylic alcohol.

Scheme 193. Efficient synthesis of 2,4-di- and trisubstituted thiazoles via p-TsOH·H₂O-catalyzed cyclization of trisubstituted propargylic alcohols.

Scheme 194. Mechanism for the synthesis of trisubstituted thiazoles.

Scheme 195. Propargylation of indoles catalyzed by p-TSA.

Scheme 196. p-TSA catalyzed synthesis of oxazoles from propargylic alcohols.

Scheme 197. TfOH catalyzed synthesis of polysubstituted furans/pyrroles from propargyl alcohols and terminal alkynes.

Scheme 198. Mechanism for the synthesis of polysubstituted furans/pyrroles from propargyl alcohols and terminal alkynes.

Scheme 199. HBF₄ as a practical catalyst for propargylation reactions.

Scheme 200. NBSA catalyzed nucleophilic substitution of propargyl alcohols.

Scheme 201. Acid-promoted intramolecular ipso-Friedel–Crafts alkylation of phenol derivatives involving propargylic substitution reaction.

Scheme 202. Mechanism for the acid-promoted fused heterocycles from propargylic alcohols.

Scheme 203. Synthesis of substituted dihydro-β-carbolines promoted by Brønsted acid.

Scheme 204. Mechanism for the synthesis of substituted dihydro-β-carbolines promoted by p-TSA.

Scheme 205. Zeolite catalyzed propargylic substitution reaction.

Scheme 206. Silica supported HClO₄ catalyzed allylation of propargylic alcohols.

Scheme 207. Phosphomolybdic acid supported on silica gel (PMA/SiO₂) for propargylic substitution.

Scheme 208. Silica supported PMA in the nucleophilic propargylic substitution reaction.

Scheme 209. Silica supported PMA for the propargylation of electron rich arenes.

Scheme 210. Mechanism for the PMA catalyzed propargylic substitution reaction.

Scheme 211. Propargylic substitution using recyclable mesoporous silica spheres embedded with Fe–Co/graphitic shell nanocrystals.

Scheme 212. K-10 catalyzed propargylic substitution reaction.

Scheme 213. Mechanism for the K-10 catalyzed propargylic substitution reaction.

Scheme 214. Zeolite as a catalyst for propargylic substitution reaction.

Scheme 215. Efficient alkylation of indoles with propargylic acetates using Amberlyst-151.

Scheme 216. Propargylation of indoles by amberlite resin catalyst.

Scheme 217. Chiral phosphoric acid catalyzed highly enantioselective synthesis of 7-alkynyl-12a-acetamido-substituted benzo[c]xanthenes in very good yields form propargylic alcohols.

Fig. 23. Transition state structure for the formation of 7-alkynyl-12a-acetamido-substituted benzo[c]xanthenes in high enantioselectivity.

Rashmi Roy

Satyajit Saha