WOLFF rearrangement distribution

The most important competition in this sequence is between the 6it cy-clization process, affording the 2-acylpyrroles 123, and the Wolff rearrangement—producing pyridones 124 via ketenes 120. The product distribution... 

Though only 100 trajectories were computed, the results with all three functionals are similar. About two-third of these trajectories led to 100 followed by the shift of the C5 methyl group. Another 15 percent led to 100 followed by the shift of the Cl methyl gronp. This distribution, consistent with the experiment that shows a preference for C5 migration, implicates a nonstatistical Wolff rearrangement. 

The effect of substituents on the temperature dependence of a-carbonyl-carbene reactivity has been examined using carbenes generated by low-temperature photolysis of methyl diazophenylacetate. A correction to the literature on the photoreaction of isopropylidene diazomalonate (98) with 1,3,3-trimethyl-cyclohexane (99) has been reported. The photoproduct, originally thought to be a cyclopropane derivative, has now been shown to be the cyclobutanone (100), the formation of which presumably involves a photo-Wolff rearrangement as illustrated in Scheme 11. Substituent effects observed in the product distribution of diazo-amide photochemistry have been ascribed to conformational factors the jS-lactam, oxindole, and Wolff rearrangement products appear to arise directly from the excited singlet state of the sym-Z form of the diazo-amide itself. 

The isomerization of the a -oxo-carbenes (197) and (199) via the oxiren (198) has been investigated, using labelled diazocarbonyl compounds as carbene sources (Scheme 10). ° The distribution of the labelled carbon in the products showed that the Wolff rearrangement proceeds in both cases, but mainly from (199). 

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