Stereoselective Synthesis of Polysubstituted Conjugated Dienes Enabled by Photo-Driven Sequential Sigmatropic Rearrangement

We here reported a highly stereoselective method for the synthesis of polysubstituted conjugated dienes from alpha-aryl alpha-diazo alkynyl ketones and pyrazole-substituted unsymmetric aminals under mild conditions, which was promoted by photo-irridation and involved with 1,6-dipolar intermediate and quadruple sigmatropic rearrangements, was successfully developed. In this transformation, the cleavage of four bonds and the recombination of five bonds were implemented in one operational step. This protocol provided a modular tool for constructing dienes from amines, pyrazoles and alpha-alkynyl-alpha-diazoketones in one-pot manner. The results of mechanistic investigation indicated that the plausible reaction path underwent the 1,6-sigmatropic rearrangement instead of the 1,5-sigmatropic rearrangement. An unprecedented photo-driven quadruple sequential sigmatropic rearrangements of alpha-aryl alpha-diazo alkynylketones with aminals via 1,6-dipolar ion intermediate is disclosed. This protocol provides a facile access to synthetically useful multi-substituted conjugated dienes in highly stereoselective manner via visible light catalysis in mild conditions.+ image