3-Aroylaziridines react with a variety of aryl isothiocyanates in refluxing benzene to give either (a) 4-aroyl-5-arylamino-4-thiazolines by a [2 + 31 cycloaddition and/or (b) 2-arylamino-4-aroyl-4-thiazolines.When the N-substituent of the aziridine is cyclohexyl or isopropyl the product type (a) is isolated in greater quantity, but when the N-substituent is methyl, product type (b) is isolated in greater quantity. The reactions provide convenient one-step syntheses of new 4-aroyl-4-thiazolines.

3-Aroylaziridines and 3-acylaziridines react with diphenylcyclopropenone with the formation of novel 4-aroyl-4-oxazolines and 4-acyl-4-oxazolines respectively. The unusual physical and chemical properties of these reactive heterocycles are discussed.

~-OXAZOLINES represent a hitherto unknown diphenylcyclopropenone (DPP) . Treatment of heterocyclic system, although they have been either cis-or trans-2-benzoyl-l-cyclohexyl-3postulated as intermediates in the Lewis acid-phenylaziridinez with one equivalent of DPP3 in catalysed rearrangement of 2-aroylaziridines, lead-refluxing benzene, followed by chromatographic ing to the formation of 3xazoles.l We report the separation, affords the 4-oxazoline (I; R 1 = Rs preparation of 4-oxazolines by the addition of = Ph, R2 = C,H,,) (46-5%), m.p. 163'; vmax azomethine ylids, derived from acylaziridines, to (CHCl,) 1695 cm.-l (C=O) ; 8Me,Si(CDClJ 2.8-3.1

Diphenylcyclopropenone reacts with 1,3-diphenylisobenzofuran to give a benzotropone derivative 5, with 3-carboalkoxyaziridines to give trans-3-pyrrolines (e.g. lo), and ~i t h a 3-cyanoaziridine to give the pyrrole 20. Possible ~nechanisms of these reactions are considered and compared with previous 1,3-dipolar additions to cyclopropenones.

2-Arenoylaziridines undergo thermal 1.3-dipolar addition to aromatic aldehydes and chloral via azomethine ylides to give exclusively 4-arenoyloxazolidines. Proof of the orientation of the addition was obtained and the formation of an alternative ring-expansion product was excluded by specific deuterium-labelling experiments. The lack of dependence of the course of the reaction on the stereochemistry of the aziridine, and the observed lack of basecatalysed epimerisation of the oxazolidines, suggested exclusive formation of the oxazolidines via the more stable trans-azomethine ylide and allowed an assignment of the full stereochemistry of the products.ADDITION reactions of substituted aziridines involving cleavage of the 2,3-bond to give an azomethine ylide intermediate and subsequent [2 + 31 cycloaddition to an acetylenic bond and to activated alkenes are synthetically useful routes to pyrroles and pyrrolines.l-14 Heat e.g. ArCH-CHAr