The N-allyl-4-oxidoanilinium ylides (1 la+) undergo a [3,2] sigmatropic rearrangement at 0 "C to give initially the products (9a-c), which undergo a further [3,3] rearrangement to give the isolated reaction products (8a-c). The N-(3,3-dimethylallyl)-4-oxidoanilinium ylide (1 1 d) reacts at 0 'C by the alternative pathway involving homolysis and radical pair recombination to give a mixture of the products (8d) and (1 3d). The ylides (1 5a-c) rearrange by a similar radical pair mechanism. The N-pentadienyl-4-oxidoanilinium ylides derived from the salts (24a and b) also rearrange at 0 'C by a sequence of [3,2] and [3,3] sigmatropic rearrangements to give in each case the product (26b). The N-allyl-3-oxidoanilinium betaines (29a and b) undergo [3,3] rearrangements on heating at 40 "C to give mixtures of the products (32) and (33) whereas the N-pentadienyl-3-oxidoanilinium ylide (30) gives only the product (35) of a [5,5] rearrangement followed by aromatisation.

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The carbonyl-stabilised ammonium ylides (3), (1 2a-n), and (14a-c) were obtained from the reaction of the corresponding ammonium halides ( l ) , (13a-n), and (1 5a-c) with sodium hydroxide in water or aqueous methanol. The ylides, which were characterised by their molecular formulae and spectroscopic properties, regenerated quaternary ammonium bromides on treatment with hydrobromic acid. In general the reactions of the ammonium ylides resemble those of the corresponding sulphonium ylides. Thus ylides having a suitable migrating group (ArCH,) undergo a Stevens [1,2] rearrangement on heating, and other ylides fragment to give a tertiary amine and products containing the PhCOCH grouping. A number of ylides reacted with dimethyl acetylenedicarboxylate to give the furans (32). The ylides (14b and c) with phenyl isocyanate gave the phenylcarbamoylsubstituted ylides (35). THE Stevens [I ,2] anionic rearrangement was discovered in 1928 when T. S. Stevens and his co-workers reported that treatment of benzyldimethyl(phenacy1)ammonium bromide (1) with warm, aqueous sodium hydroxide gave the amino-ketone (2). that the ylide (3) was an intermediate in the reaction (1)+(2), but ammonium ylides closely analogous to (3) which are able to undergo a [1,2] rearrangement had not been isolated before the work described in this paper was initiated, although stable phosphonium and sulphonium ylides were well known. Furthermore, the acidity constants for the sulphonium salt (4a) (pK, 6.66) and the phosphonium salt (4b) (pKa 7.75) are significantly lower than that of the analogous Stevens subsequently proposed PhCH2&Me *CH2COPh BrPhCH2CHCOPh I NMe2 + -PhCH2N Me 2CHCOPh Ph -\ + -/ Ph XCHCOPh \+ / XCH2COPh Br Me Me I 4 1 a ; X = S b ; X = PMe c ; X = NMe ammonium salt (4c) (pK, 9.8) suggesting tliat the stabilities of the corresponding ylides ( 5 ) would decrease in the order (5a) > (5b) (5c). I t had been shown 4,5 that $-c and 6-c bond lengths were significantly shorter in these ylides than the normal P-C and S-C single bond lengths, in accord with the t Part 7, T. Laird, W. D. Ollis, and I. 0. Sutherland, J.C.S. Perkzn 1, 1980, 2033. view tliat d,,-b,, bonding might be involved in the presumed greater stability of (5a) and (5b) as compared with (5c). Pyridinium ylides [e.g. (S)] were, however, I CHCOR II CHCOR I -CHCOR ( 6 a ) ( 6b) ( 6 c ) F F 9 NMe,Ar Me2NCHCOAr 1 + -(10 1 well known but simple resonance considerations show that these have greater possibility for charge delocalisation, as indicated by the canonical forms (sa), (6b), and (6c), than analogous ammonium ylides [e.g. (3)], an effect that was supported by studies of acidity constants. A few simple ammonium ylides had been isolated,7-9 but these were limited to rather special cases such as the ylides (7)-(10). More recently the highly fluorinated ylide (1 1) has also been described.1°The isolation of ammonium ylides analogous to (3) was therefore of interest because of our studies of the related I-Z,2] and [3,21 sigmatropic rearrangements of allylic ammonium ylides,ll and th...

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