The use of chiral auxiliaries for the preparation of non-racemic substrates is a well-developed branch of organic synthesis. Methods for the attachment of chiral auxiliaries to organic substrates, their subsequent use as stereocontrol elements in chemical reactions, and their ultimate removal are both diverse and sophisticated. The Evans' oxazolidinone-based auxiliaries, developed more than thirty years ago, are the standard bearer in stereoselective synthesis and they have recently been used for intermolecular [4+2] cycloaddition reactions involving dienes and terminal alkynamides. We report herein an extension of this methodology to intramolecular substrates. We will describe general reaction conditions in which the tether length is varied, the atom composition of the tether is varied, and the size of the chiral group is modulated to maximize diastereoselectivity in an intramolecular [4+2] cycloaddition. Further conversion of these products to enantiopure fused- and/or bicyclic ketones and their subsequent elaboration to bioactive molecules will be reported.

Chiral alkynamides as substrates for intramolecular [4+2] cycloadditions

245th National Meeting (2013)

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