Abstract
Abstract The cycloaddition reactions of dimethyl 1-oxo-(E,E)-2,4-hexadiene phosphonate (1) with 2-alkylidene-1,3-dithianes 4 and 5 gave [1]oxa-[7,11]dithiaspiro-[5,5]undecene-2-phosphonate derivatives. The reactions were responsive to electrophilic assistance by the solvent as well as ‘conventional’ Lewis Acid catalysis. The structural constitutions and preferred conformations of these pyran derivatives were established by NMR spectroscopy as well as by the X-ray crystallographic determination of a key derivative. In addition to E- to Z-double bond isomerization reactions in 1 and acyl chloride 2, αacyl phosphonate 1 underwent thermal isomerization to dimethyl 2H-pyran-6-phosphonate (6).
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