ALKALI METAL DERIVATIVES OF GROUP IV ORGANOMETALLICS: MECHANISTIC ASPECTS OF REACTIONS WITH HALIDES
Organometallic derivatives of the Group IV elements have been known and used as synthetic intermediates for a half century, but little has been done by way of systematic investigation of the scope, and limitations of their reactions. And only recently have investigators turned their attentions to the study of mechanistic aspects of these reactions. An overview of the field reveals many highly useful facts, but it is also strewn with some contradictory observations, along with many others that are difficult to fit into a coherent overall conceptual scheme. This scheme lies beyond the present horizon and will be revealed only after completion of systematic studies on the various parameters affecting the scope, limitations, and mechanisms of these reactions. Delineation of these, in turn, will provide reliable guides to their synthetic utility. This report deals with our present understanding of the mechanisms of Group IV organometalalkalis with organic halides, with reference to other reactions as appropriate, and with some of the questions concerning these reactions, whose answers lie beyond the horizon. Experimental observations which are relevant for understanding of mechanisms will be first summarized; mechanisms consistent with these will be reviewed; and questions remaining to be answered will be raised. Because of the nature of the presently known facts, those concerning silicon, germanium, tin, and lead alkalis will be intermingled, and valid trends within the series will be indicated.
Mise en evidence d'un mecanisme de substitution arynique pour la reaction d'halogenures aromatiques avec le tributylstannyllithium
Abstract Evidence for a benzyne mechanism is observed when tributylstannyllithium reacts with aromatic fluorides and chlorides, however with the corresponding bromides the reaction fails to proceed by this mechanism.
Investigations on organolead compounds II. The reaction of triphenylplumbyllithium with small-ring heterocycles: Functionally substituted organolead compounds
Abstract The reactions between triphenylplumbyllithium and small-ring heterocycles have been studied. The reaction ran successfully with the following heterocycles: ethylene oxide, ethylene V83 V 2 sulphide, N -acylethylenimines and trimethylene oxide. No reaction occurred with ethylenimine, N -butylethylenimine, trimethylene sulphide and tetrahydrofuran. Some substituted rings also reacted in the expected way: epichlorohydrin gave a linear product, Ph 3 PbCH 2 CHOHCH 2 Cl, and β-propiolactone gave primarily Ph 3 PbCH 2 CH 2 COOH, which, however, spontaneously lost one molecule of benzene to give [Ph 2 Pb - CH 2 CH 2 COO - ] ; with diazomethane the acid could be trapped as the methyl ester. Ketene dimer and pyrrolidone caused decomposition of triphenylplumbyllithium. Treatment of the epichlorohydrin product, Ph 3 PbCH 2 CHOHCH 2 Cl, with one equivalent of hydrogen chloride resulted in the elimination of the CH 2 CHOHCH 2 Cl group; whereas chlorination led merely to elimination of phenyl groups. This discrepancy is explained by assuming that protonation of the hydroxyl group (in case of treatment with hydrogen chloride) facilitates separation of the CH 2 CHOHCH 2 Cl group.