STEREOSELECTIVE PROTONATION OF CARBANIONS.1. DIASTEREOSELECTIVE PROTONATION OF C-H-ACTIVATED CYCLOHEXANE DERIVATIVES

The diastereoselectivity of the kinetically controlled protonation of carbanions derived from 4-tert-butyl-1-X-cyclohexanes (1: X = CN, 2: X = CO2Me, 2-Si: X = C(OMe)OSiMe3, 3: X = COPh, 4: X = SO2Ph) is system atically investigated. By variation of (a) the base for deprotonation of 1-4, (b) OH-, NH-, and CH-proton sources, (c) added salts, Lewis ba ses, and acids, (d) solvents (cf. Tables 2-5) the cis/trans ratios of diastereomers could be influenced as follows: 1: 41/59 --> 85/15; 2: 2 6/74 --> 73/27; 3: 26/74 --> 93/ < 3; 4: 1/99 --> 37/63. The results a re discussed with regard to structure and aggregation of 1Li to Li-4 a nd compared with relevant data from the literature. It is concluded th at so far dn empirical approach to high diastereoselectivities cannot be avoided and that the results cannot be predicted from the ratios ob tained by the much slower alkylation reactions.