Organosulfur chemistry. II. Highly stereoselective reactions of 1,3-dithianes. Contrathermodynamic formation of unstable diastereoisomers
作者:Ernest L. Eliel、Armando A. Hartmann、Anthony G. Abatjoglou
DOI:10.1021/ja00813a026
日期:1974.3
contrathermodynamic'' equilibration occurs with the equatorial carbinols mentioned, above, with r-2-tert-butyl-cis-4,cis-6-dimethyl-1,3dithiane and with cis-2,4,4,6-tetramethyl-1,3-dithiane, suggesting a very large preference of the intermediate 2-dithianyl-lithium compound to have the metal in the equatorial position. The high degree of this preference (over 6 kcal/mol) suggests operation of a stereoelectronic
用 DCl 处理 cis-4,6-二甲基-1,3dithiane (1) 的锂衍生物几乎完全(超过 99%)得到赤道 2-氘代化合物 (1a),用碘甲烷处理完全得到赤道甲基化合物(r-2,cis-6,cis-4trimethyl-1,3-dithiane, 2) 和羰基化合物(甲醛、丙酮和新戊醛)处理得到至少 99.8% 异构体纯度的赤道甲醇 (4) . 用HCl处理赤道2-甲基化合物2的锂衍生物仅产生相应的轴向异构体3(r-2,反-4,反-G-三甲基-1,3-二噻烷);上面提到的赤道甲醇、r-2-叔丁基-cis-4,cis-6-dimethyl-1,3dithiane 和cis-2,4,4,6-tetramethyl 会发生类似的逆热力学平衡-1,3-二噻烷,这表明中间体 2-二噻吩基锂化合物非常倾向于在赤道位置具有金属。这种偏好的高度(超过 6 kcal/mol)表明是立体电子而不是简单的空间效应的操作。2