The π-route to substituted adamantanes. Part II.
Abstract
Cyclisation of 2-(endo-bicyclo[3,3,1]non-6-en-3-yl)propan-2-ol in hot formic acid yields, after hydrolysis of the initial product, a mixture of 4,4-dimethyladamantan-2ax- and -2eq-ol of which the latter, derived from trans-addition to the double bond, predominates by a factor of 6 : 1. These stereochemical assignments are based on the n.m.r. spectra of the isomers in pyridine solution as compared with dimethyl sulphoxide solution and on the production of the axial alcohol by reduction of 4,4-dimethyladamantan-2-one with lithium aluminium hydride. Cyclisation of 2-(endo-bicyclo[3,3,1 ]non-6-en-3-yl)propan-2-ol in 98% sulphuric acid at 20° yields a 1 : 3 mixture of 2,2-dimethyladamantan-1-ol and 4,4-dimethyladamantan-1-ol, whereas in this medium at 50° the major product is 3,5-dimethyladamantan-1-ol; these products are formed by intermolecular hydride transfer and skeletal re-arrangement reactions after π-route cyclisation has occurred. In hot formic acid, α-(endo-bicyclo[3,3,1]non-6-en-3-yl)benzyl alcohol yields, after hydrolysis of the formate, 2-phenyladamantan-1-ol.