(Acyloxy)carbenes from Thermolysis of Oxadiazolines in Solution. 1-Acetoxyethylidene and 1-Acetoxypropylidene

Article abstract of DOI:10.1021/jo00146a010

Thermolysis of 2-acetoxy-5,5-dicyclopropyl-2-methyl-Δ³-1,3,4-oxadiazoline in CCl4 at 79.5 deg C afforded biacetyl, acetyl chloride, and dicyclopropyl ketone, among other products.It is proposed that the oxadiazoline loses nitrogen, in the first step, to form a carbonyl ylide.The latter then fragments, primarily to dicyclopropyl ketone and 1-acetoxyethylidene <(acetoxymethyl)carbene>.That carbene is partitioned between 1,2 acyl transfer to form biacetyl and abstraction of Cl from CCl4 to form 1-acetoxy-1-chloroethyl radical.The latter undergoes β scission to formacetyl chloride and acetyl radical, which in turn abstracts from CCl4 to form more acetyl chloride.Similarly, 2-acetoxy-5,5-dicyclopropyl-2-ethyl-Δ³-1,3,4-oxadiazoline decomposed in CCl4 to form 2,3-pentanedione, acetyl chloride, propionyl chloride, dicyclopropyl ketone, and other products.Again, the α-diketone is accounted for in terms of an (acyloxy)carbene precursor (1-acetoxy-1-propylidene) and the formation of two acyl chlorides supports the hypothesis that such a carbene can abstract Cl from CCl4, with subsequent β scission of the resulting radical. 1-Acetoxyethylidene was trapped with neat 2-acetoxypropene and with neat 2-methoxypropene to form cyclopropanes.