Stereoselectivity and stereospecificity in electron deficient diene cycloadditions with norbornadiene and 7-t-butoxynorbornadiene: results and MINDO/2 theoretical study

Abstract

Unlike norbornadiene, which reacts stereospecifically with cyclopentadiene and cyclopentadienone derivatives in inverse electron demand [_π4_s+_π2_s] cycloadditions (giving the endo-exo-series of adducts), 7-t-butoxynorbornadiene exhibits stereoselectivity for the endo-syn-mode in similar cycloadditions, giving an anti-t-butoxy endo-endo-adduct as the major (periselective) component of the product mixtures. MINDO/2 Calculations indicate that the olefinic site of addition syn to the bridge alkoxy group is the HOMO (as required by qualitative cycloaddition theory), and also that the π orbital coefficients are larger than in norbornadiene. ¹H and ¹³C n.m.r. data for the various adducts are tabulated and mass spectral data are also recorded.