Six-membered Nitrogen- and Oxygen-containing Rings

Six-membered Nitrogen- and Oxygen-containing Rings. The cycloaddition between aroyl isothiocyanates and NN-disubstituted hydrazones, especially of cyclanones, gives unstable derivatives of 1,3,5-oxadiazine (147).  

Christo], D. Fevrier-Piffaretti, and Y. Pietrasanta, Bull. Soc. chim. France, 1972, 

The structures of the products have been elucidated and a two-step mechanism is suggested. 

Eschenmoser s group have investigated the Ag+-induced cycloaddition reactions of a-chloro-aldonitrones (150). The a-chloro aldonitrone-Ag+ system is a powerful enophile, reacting with oleiins that would normally be expected to be inactive in [4 + 2]cycloadditions. The products from the reaction can be converted efficiently into y-lactones, e.g. (151), or the reaction may be used to cleave a double bond oxidatively whilst extending the length of a carbon chain, e.g. (152) — (153). The sequence of reactions in the latter case is (i) [2 + 4]cycloaddition, (ii) deprotonation, (iii) [2 + 4 1-cycloreversion. 

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