Diaryl hypervalent bromines and chlorines: synthesis, structures and reactivities

Abstract

In the field of modern organic chemistry, hypervalent compounds have become indispensable tools for synthetic chemists, finding widespread applications in both academic research and industrial settings. While iodine-based reagents have historically dominated this research field, recent focus has shifted to the potent yet relatively unexplored chemistry of diaryl λ³-bromanes and -chloranes. Despite their unique reactivities, the progress in their development and application within organic synthesis has been hampered by the absence of straightforward, reliable, and widely applicable preparative methods. However, recent investigations have uncovered innovative approaches and novel reactivity patterns associated with these specialized compounds. These discoveries suggest that we have only begun to tap into their potential, implying that there is much more to be explored in this captivating area of chemistry.

Fig. 1. Halogen-based hypervalent molecules feature a 3c–4e bonding.

Fig. 2. Periodic table properties of halogens.

Scheme 1. Synthesis of cyclic hypervalent bromines and chlorines.

Scheme 2. Synthesis of tetrafluoroborate (BF₄⁻) and hexafluorophosphate (PF₆⁻) salts of 2.

Scheme 3. Synthesis of diaryl λ³-bromanes and chloranes.

Scheme 4. Direct oxidation of 15 and 16.

Scheme 5. Preparation of λ³-bromanes and chloranes.

Fig. 3. X-ray structure of 17.

Scheme 6. Synthesis of diaryl λ³-bromane 28.

Fig. 4. X-ray structure of 28.

Scheme 7. Synthesis of diaryl λ³-bromane 30.

Fig. 5. X-ray structure of 30.

Scheme 8. Preparation of diaryl λ³-halogens.

Fig. 6. X-ray structure of 36.

Scheme 9. Structure and orbital correlation.

Scheme 10. Synthesis of cyclic diaryl λ³-bromanes.

Scheme 11. Synthesis of cyclic diaryl λ³-bromanes.

Scheme 12. Synthesis of chiral cyclic diaryl λ³-bromanes.

Fig. 7. X-ray structure of 46.

Scheme 13. Synthesis of chiral cyclic diaryl λ³-halogens.

Scheme 14. Synthesis of cyclic diaryl λ³-chloranes.

Fig. 8. X-ray structures of 4-BF₄, 2-OMs and 58.

Scheme 15. Synthesis of cyclic diaryl bis λ³-halogenum.

Fig. 9. X-ray structures of 60 and 61.

Scheme 16. Reactivity of diaryl λ³-bromanes and chloranes.

Scheme 17. Reactivity of diaryl bis λ³-halogens with rhodanide and benzenesulfinate.

Scheme 18. Reactivity of phenyl(m-carboran-9-yl)halogen compounds with various nucleophiles.

Scheme 19. Reactions of phenyl(m-carboran-9-yl)halogen tetrafluoroborates with PPh₃.

Scheme 20. Reactivity of diaryl λ³-chloranes with various nucleophiles.

Scheme 21. Photo-initiated polymerization using diaryl λ³-halogen compounds.

Scheme 22. Photo-degradation of diaryl λ³-halogen compounds.

Scheme 23. Pyrolysis of diaryl λ³-bromane and chlorane compounds.

Scheme 24. Mechanistic investigation of the reactivity of cyclic diaryl λ³-bromane and chlorane compounds.

Fig. 10. Calculated energy diagram (in kcal mol⁻¹) for the formation of arynes from hypervalent halonium.

Scheme 25. Cycloadditions with cyclic diaryl λ³-bromanes.

Scheme 26. Reactivity of cyclic diaryl λ³-bromanes and chloranes towards carboxylic acids, anilines, amines and phenols.

Scheme 27. Reactivity of cyclic diaryl λ³-bromanes towards alcohols.

Scheme 28. Cyclic diaryl λ³-bromane catalysed Michael reaction.

Scheme 29. Enantioselective Mannich reaction catalysed by cyclic diaryl λ³-bromanes.

Scheme 30. Enantioselective Mannich reaction catalysed by N-nitrosamine cyclic diaryl λ³-bromanes.