Preparation of donor‐acceptor‐substituted vinylcyclobutanes

2‐Methylen‐1,3‐dioxolane ( 1 ) and the methyl acrylates or crotonates 2 form [2+2] cycloadducts 3 which are reduced to give alcohols 6 . Oxidation of these alcohols at low temperatures leads to unstable aldehydes 7 , which either rearrange to dihydropyrans 5 or react with Wittig(‐Horner) reagents to afford donor‐acceptor‐substituted vinylcyclobutanes 8 . The cis ‐vinylcyclobutane 8g is prepared by [2+2] cycloaddition of dioxolane 1 and methyl (2 E ,4 Z )‐hexadienoate ( 9 ). The configurations and preferred conformations of the vinylcyclobutanes 8 have unequivocally been assigned on the basis of 13 C‐and 1 H‐NMR spectra.