REGIOSELECTIVITY AND STEREOSELECTIVITY IN UNCATALYZED AND CATALYZED DIELS-ALDER REACTIONS OF ALLENIC ESTERS WITH FURAN AND 2-METHYLFURAN

Complete regio- and stereo-selectivity in both uncatalysed and catalysed t 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.