Reactions of (Organostannyl)- and (Organogermyl)lithium Reagents with Some (Allylic) Cyclohex-2-enyl Chlorides

Article abstract of DOI:10.1021/jo00146a014

The stereo- and regiochemistries of the reactions between (trimethylgermyl)lithium, (triphenylstannyl)lithium, and (trimethylstannyl)lithium and cis- and trans-5-methyl-2-cyclohexenyl chlorides, 3,5-dimethyl-2-cyclohexenyl chlorides, and some deuterated derivatives have been investigated utilizing 1H, 2H, 13C, and 119Sn nuclear magnetic resonance spectroscopy.The major substitution pathway (forming the allylic organometallic) involves configurational inversion at carbon and is accompanied by an insignificant level of 2H relocation between the allylic positions.The S_N2 mechanism is strongly implicated.Serious side reactions accompany the reactions of (trimethylgermyl)lithium generated in hexamethylphosphoric triamide (HMPA), and significant amounts of digermanes and cyclohexenyldimethylamines form.The latter almost certainly result from chloride displacement by dimethylamide ((CH3)2N:^-, formed by alkali metal cleavage of HMPA), such displacement proceeding regio- and stereospecifically in accord with the S_N2 pathway.Pentamethyl(cyclohex-2-enyl)digermanes which are formed stereospecifically, are considered to result from chloride displacement by (pentamethyldigermyl)lithium, formed by dimethylgermylene insertion into (trimethylgermyl)lithium itself.Certain redistribution reactions of the pentamethyl(cyclohex-2-enyl)digermanes have been observed.