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. 2013 Apr 30:9:838-45.
doi: 10.3762/bjoc.9.96. Print 2013.

Diastereoselective synthesis of nitroso acetals from (S,E)-γ-aminated nitroalkenes via multicomponent [4 + 2]/[3 + 2] cycloadditions promoted by LiCl or LiClO4

Leandro Lara de Carvalho  1 , Robert Alan Burrow, Vera Lúcia Patrocinio Pereira
Affiliations

Diastereoselective synthesis of nitroso acetals from (S,E)-γ-aminated nitroalkenes via multicomponent [4 + 2]/[3 + 2] cycloadditions promoted by LiCl or LiClO4

Leandro Lara de Carvalho et al. Beilstein J Org Chem. .

Abstract

Chiral nonracemic aminated nitroso acetals were synthesized via diastereoselective multicomponent [4 + 2]/[3 + 2] cycloadditions employing new (S,E)-γ-nitrogenated nitroalkenes 5a-c as heterodienes, ethyl vinyl ether (EVE) as a dienophile, and selected electron-deficient alkenes as 1,3-dipolarophiles. The employment of different organic solutions of LiClO4 or LiCl as promoter systems provided the respective nitroso acetals with yields from 34-72% and good levels of diastereoselectivity. In addition, the nitroso acetal 9c was transformed to the pyrrolizidin-3-one derivative 14c, proving the usefulness of the route in the synthesis of an interesting chiral compound. The elucidation of the stereostructures was based on 2D COSY, NOESY and HSQC NMR experiments as well as an X-ray diffraction experiment.

Keywords: chiral heterodiene; hetero-Diels–Alder reaction; pyrrolizidin-3-one; solvent effect; tandem reaction.

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Figures

Scheme 1
Scheme 1
Reactivity of nitroalkenes and/or their respective nitronates in cycloaddition reactions.
Scheme 2
Scheme 2
Synthetic route toward the chiral (S,E)-γ-aminated nitroalkenes 5a–c and their 1,3-diamine derivatives.
Figure 1
Figure 1
ORTEP for nitroso acetal 11b.
Figure 2
Figure 2
1D NOESY correlation between H2, H3a, H4 and H6 for all nitroso acetals.
Scheme 3
Scheme 3
Transition-state models to stereoselective approaches in the multicomponent cycloadditions of 5a–c.
Scheme 4
Scheme 4
Hydrogenolysis of 9c to pyrrolizidin-3-one 14c.
See this image and copyright information in PMC

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