Asymmetric [4 + 2] annulation of 5H-thiazol-4-ones with a chiral dipeptide-based Br?nsted base catalyst?

Chemical Science Pub Date: 2016-06-09 DOI: 10.1039/C6SC02039A

Abstract

Versatile synthetic strategies that access diverse chemical substrates in a highly chemo- and stereo-selective manner are crucial but demanding. Construction of chiral molecules with multiple (hetero)-quaternary carbon stereocenters in a single fashion is a particularly significant challenge, with important applications in the synthesis of a range of bioactive compounds containing the 1,4-sulfur bridged piperidinone structural motif. The asymmetric synthesis of these entities is complicated due to the need to build at least two hetero-quaternary stereocenters concurrently. In order to achieve this, we have developed a new family of dipeptide-based multifunctional Br?nsted base organocatalysts that are highly capable of the first asymmetric [4 + 2] annulation reaction of 5H-thiazol-4-ones with electron-deficient alkenes. This protocol could be applied to a series of alkenes such as nitroalkenes, 4-oxo-4-arylbutenones, 4-oxo-4-arylbutenoates and methyleneindolinones, providing an efficient approach to valuable chiral 1,4-sulfur bridged piperidinones and their derivatives with multiple hetereo-quaternary stereogenic centers in high yields and enantioselectivities. Density functional theory studies involving 5H-thiazol-4-one and nitroolefin catalysis propose stereochemical insights into the origin of enantio- and chemo-selectivity.

Graphical abstract: Asymmetric [4 + 2] annulation of 5H-thiazol-4-ones with a chiral dipeptide-based Br?nsted base catalyst
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