Chapter 4 Four-membered ring systems

Abstract

This chapter provides information on four-membered ring systems. The chapter discusses: (1) azetines and azetidines; (2)oxetanes, 2-oxetanones, thietanes and benzothietes; (3) dioxetanes, diazetanes and dithietanes; (4) phosphorus and silicon heterocycles; and (5) azetidinones (β-lactams). Mixtures of the cis and trans isomers of 2,3,4-trisubstituted azetine, together with the isoquinoline, are obtained on photolysis of α-dehydrophenylalanine amides. β-Lactones have also been obtained from reactions involving loss of dinitrogen from other heterocycles. The mechanism suggested involves photoacetyl migration. Other thietane derivatives have been obtained by isomerization of nitrogen-containing heterocycles. The reaction of an acyl isothiocyanate (RCONCS) with diphenyldiazomethane gave the isomerized in solution to the tetraphenyl-3- thietanone. The blue fluorescence of dioxetane (X = O and CH 2 , R = alkyl) in the presence of fluoride ion has been discussed. X-Ray crystal structures are available for the novel diazaphosphete. The migratory aptitude of substituents on the disilylcarbene generated by photolysis has been discussed. The use of chiral auxilliaries in the Staudinger reaction has been explored extensively.