Tandem Inter [4 + 2]/Intra [3 + 2] Nitroalkene Cycloadditions. 5. Origin of the Lewis Acid Dependent Reversal of Stereoselectivity

Scott E. Denmark, Mark E. Schnute, C. B.W. Senanayake

Research output: Contribution to journalArticle

Abstract

The stereochemical course of the tandem [4 + 2]/[3 + 2] nitroalkene cycloaddition with chiral enol ethers has been shown to exhibit remarkable sensitivity to the nature of the Lewis acid promoter. Cycloadditions using (+)-camphor-derived vinyl ether 3 or (−)-trans-2-phenylcyclohexanol-derived vinyl ether 6 gave a predominance of the 1S hydroxy lactam 4 when promoted by Ti(O-i-Pr)2Cl2. The same vinyl ethers selectively produced the 1R hydroxy lactam 4 when promoted by MAPh. The (E)- and (Z)-1-propenyl ethers of (−)-trans-2-phenylcyclohexanol have been used to investigate the reversal of selectivity. Cycloadditions promoted by Ti(O-i-Pr)2Cl3 were found to be endo selective (12:1), while MAD and MAPh favored exo approach of the dienophile. High levels of asymmetric induction were observed in the endo mode of the cycloaddition for propenyl ethers (E)-13 and (Z)-13, 97.9% ee and 82.2% ee, respectively, but an erosion of selectivity occurred in the exo mode (72.2% ee) presumably through an s-cis enol ether conformation.

Original languageEnglish (US)
Pages (from-to)1859-1874
Number of pages16
JournalJournal of Organic Chemistry
Volume58
Issue number7
DOIs
StatePublished - Jan 1 1993

ASJC Scopus subject areas

  • Organic Chemistry

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