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Abstract
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Alkyl isocyanides react with dialkyl acetylendicarboxylates in the presence of CH-acids such as cyclopentane-1,3-dione, cyclohexane-1,3-dione, or 5,5-dimethylcyclohexane-1,3-dione to afford highly functionalized 4H-pyrans in fairly high yields. In the case of reaction between dimethyl acetylenedicarboxylate and 5,5-dimethylcyclohexane-1,3-dione in the presence of cyclohexyl isocyanide or benzyl isocyanide, in addition to the 4H-pyran system, tetrahydro-cyclopenta[b]pyran derivatives were isolated. The free energy barrier (96.9 ± 2 kJ mol-1) for restricted rotation around the polarized double bond of the enaminone moiety in dimethyl 2-[cyclohexylamino-(4,4-dimethyl-2,6-dioxo-cyclohexylidene)-methyl]-but-2-enedioate was determined by dynamic NMR spectroscopy.
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