Phase-transfer-catalysed asymmetric synthesis of tetrasubstituted allenes

Abstract

Allenes are molecules based on three carbons connected by two cumulated carbon–carbon double bonds. Given their axially chiral nature and unique reactivity, substituted allenes have a variety of applications in organic chemistry as key synthetic intermediates and directly as part of biologically active compounds. Although the demands for these motivated many endeavours to make axially chiral, substituted allenes by exercising asymmetric catalysis, the catalytic asymmetric synthesis of fully substituted ones (tetrasubstituted allenes) remained largely an unsolved issue. The fundamental obstacle to solving this conundrum is the lack of a simple synthetic transformation that provides tetrasubstituted allenes in the action of catalysis. We report herein a strategy to overcome this issue by the use of a phase-transfer-catalysed asymmetric functionalization of 1-alkylallene-1,3-dicarboxylates with N-arylsulfonyl imines and benzylic and allylic bromides. Substituted allenes with axial chirality are of great utility in organic chemistry owing to their unique structure and reactivity, but synthetic methods to access them are limited. Here, a catalytic asymmetric synthesis of tetrasubstituted allenes is described that builds on the use of phase-transfer-catalysed asymmetric functionalization of 1-alkylallene-1,3-dicarboxylates.

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Hashimoto, T., Sakata, K., Tamakuni, F. et al. Phase-transfer-catalysed asymmetric synthesis of tetrasubstituted allenes. Nature Chem 5, 240–244 (2013). https://doi.org/10.1038/nchem.1567

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