Preparation of donor‐acceptor‐substituted vinylcyclobutanes

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Abstract
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 (2E,4Z)‐hexadienoate (9). The configurations and preferred conformations of the vinylcyclobutanes 8 have unequivocally been assigned on the basis of 13C‐and 1H‐NMR spectra.