Imine compounds seven-membered rings

Classical ring expansion methodology has been used to prepare the 1,4-oxazepinone 132 (X = O) and 1,4-thiazepinone 132 (X = S) derivatives from the corresponding oximes 129 prepared in turn from 128. The seven-membered ring compounds were then converted into the imines 132 in a three-step sequence via 131 <04BMCL5907>. 

Analogous to the photochemistry of A -oxides,167 the formation of the seven-membered ring occurs via an intermediate diaziridine which isomer-izes in a thermal reaction [Eq. (21)]. Although direct proof of this intermediate is not yet available, diaziridines are isolable on irradiation of analogous compounds with the azomethine imine structure.158 This supports the pathway proposed for the heterocyclic A-imines. 

Other advances include the construction of seven- and nine-membered rings via the analogous [4-1-3] and [6-1-3] cycloadditions with dienes and trienes respectively. Heterocycles, such as tetrahydrofurans and pyrrolidines, are accessible using carbonyl compounds and imines as substrates. The following discussion is organized around these recent discoveries. It serves to illustrate the versatility and the high degree of selectivity which are some of the distinctive features of the Pd-TMM chemistry. 

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