The high-pressure [4+2]cycloaddition of 1-methoxybuta-1,3-diene to the glycolaldehyde-derived heterodienophiles, catalyzed by chiral metallosalen complexes

Abstract

A high-pressure (ca. 10 kbar) reaction of 1-methoxybuta-1,3-diene 1 with variously O-protected glycolaldehydes 2, catalyzed by the chiral (salen)Cr(III)Cl 4a– d and 5 or (salen)Co(II) 6a– f and 7 complexes, has been studied. The best results were obtained for tert-butyldimethylsilyloxyacetaldehyde 2a. The reaction afforded, in good yield (up to 90%) and with very good diastereoselectivity (up to 92%) and enantioselectivity (up to 93% ee), the [4+2]cycloadducts 3a, which are compounds of significant synthetic interest. The stereochemical model of the cycloaddition reaction is discussed.