Gold-Catalyzed and IBr-Promoted Tandem Cyclization of 1,5-enynes Leading to Highly Stereocontrolled Synthesis of Functionalized Cyclohexenes

Abstract

PartⅠ. Gold-Catalyzed Tandem C-C and C-O Bond Formation: A Highly Diastereoselective Formation of Cylclohex-4-ene-1,2-diol Derivatives Gold-catalyzed tandem cyclization allows efficient transformation of tert-butyl carbonate derivatives of hex-1-en-5-yn-3-ol into densely functionalized cyclohex-4-ene-1,2-diol derivatives. A multiple of stereocenters and functionalities are generated in a single step, including a tertiary alcohol center. This protocol has a advantage of a low catalyst loading, mild reaction condition and high diastereoselectivity. The synthetic utility of the current protocol is demonstrated in the ring expansion chemistry into 7,5- and 8,5-fused bicyclic compounds, employing this tandem cyclization as a key step. Part II. Diastereoselective Tandem Iodocarbonatations of 1,5-Enynes A diastereoselective tandem iodocarbonatation of 1,5-enyne by IBr as inexpensive reagent is described. The normal chemoselectivity of iodonium reagent for alkene is reversed favoring alkyne activation in the presence of aryl group at alkyne terminus, resulting in a stereoselective tandem C-I, C-C, C-O bond formations. The resulting product has a vinyl iodide moiety for a useful subsequent transformation. For example, pseudo-biaryl compounds were synthesized by this protocol, which could be useful precursor of saturated analog of MOP ligand. In addition, a variety of other nucleophiles for a cation-trap and a range of substrates were explored along the line.