Unsaturated carbonyl compounds betaine

Dimethylsulfonium methylide is both more reactive and less stable than dimethylsulfoxonium methylide, so it is generated and used at a lower temperature. A sharp distinction between the two ylides emerges in their reactions with a, ( -unsaturated carbonyl compounds. Dimethylsulfonium methylide yields epoxides, whereas dimethylsulfoxonium methylide reacts by conjugate addition and gives cyclopropanes (compare Entries 5 and 6 in Scheme 2.21). It appears that the reason for the difference lies in the relative rates of the two reactions available to the betaine intermediate (a) reversal to starting materials, or (b) intramolecular nucleophilic displacement.284 Presumably both reagents react most rapidly at the carbonyl group. In the case of dimethylsulfonium methylide the intramolecular displacement step is faster than the reverse of the addition, and epoxide formation takes place. 

Phenyl dichlorophosphate, 240 Other P-substituted-a, P-unsaturated carbonyl compounds (E)-(Carboxyvinyi)trimethylammo-nium betaine, 67... 

Z-l,2-borylphosphinoalkenes with carbonyl compounds and ketenimines. Two reports of the reactions of (trimethylsilyl)phosphines with a,p-unsaturated carbonyl compounds have appeared. These reactions usually lead to transfer of a trimethylsilyl group from phosphorus to oxygen, presumably via the intermediacy of a phosphonioenolate betaine, the initial product of nucleophilic attack by the phosphine at the P-carbon. However, other pathways also arise in the reactions of sterically crowded organotrimethylsilylphosphines, and transfer of a trimethylsilyl group from phosphorus to the a-carbon has been observed. " ... 

The iV-propargylaminophosphines (78) readily rearrange to give the azabuta-dienylphosphine (79) via intramolecular nucleophilic attack of phosphorus at the terminal acetylenic carbon. Full details have now appeared of the reactions of 2 -1,2,3-diazaphosphole derivatives (80) with alkyl halides, giving 2,3-disub-stituted indoles as the major product. Several examples of the attack of phosphines at carbon of a, -unsaturated carbonyl compounds have been described. The betaine (81) is the active intermediate in the triphenylphosphine-induced polymerization of maleic anhydride. Phosphines also catalyse the... 

LeBerre and Renault have utilized 2-amino-1-pyrroline (30) in condensation reactions with a,/3-unsaturated carbonyl derivatives and -di-carbonyl compounds to prepare a wide variety of partially saturated pyrrolol 1,2-aIpyrimidines in which the pyrrole portion of the molecule is always completely saturated. For example, condensation of the amino-pyrroline (30) with substituted maionic esters (29) affords13,14 2-hydroxy-4,6,7,8-tetrahydropyrrolo[l,2-a]pyrimidin-4-one (31a). Spectral data indicate the betaine form (31b) to be preferred [Eq. (5)]. 

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