| Popis: |
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. |
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