Regio- and stereo-selectivity in uncatalysed and catalysed Diels–Alder reactions of allenic esters with furan and 2-methylfuran

Abstract

Complete regio- and stereo-selectivity in both uncatalysed and catalysedt Diels–Alder additions of furan to the allenic esters (1a–e), and of 2-methylfuran to the allenic esters (1b, c) has been determined through detailed ¹H and ¹³C NMR spectral investigations. Eu(fod)₃ and Pr(fod)₃ have been found to be very useful mild Lewis acid catalysts for these cycloadditions; several mol % of these reagents significantly enhance the selectivity and yield of these reactions without adversely affecting the fragile functionalities. A rationalization of the observed regio- and stereoselectivity and reactivity profile, based on the stereoelectronic factors operating in the transition states is given.