Adamantane chemistry. Part 3. Abnormal hypoiodite reactions of 2-substituted adamantan-2-ols; synthetic routes to 4-oxahomo- and 2-oxa-adamantanes, and 7-substituted-bicyclo[3.3.1]nonan-3-ols

Abstract

Reaction of 2-methyladamantan-2-ol (1a) with lead tetra-acetate and iodine in boiling benzene did not yield the expected radical fragmentation product (3a), but rather a yellow, crystalline di-iodo-ether which was previously assigned structure (4) on the basis of chemical degradative evidence and on an apparent m/e 418 molecular ion (electron impact). Structure (4) is not supported by the spectroscopic data, and ¹³C n.m.r. studies on an isotopically enriched sample of the di-iodo-ether indicate the structure to be (5b). Re-investigation of the mass spectrum has revealed that the (fairly intense) molecular ion has m/e 416; previous assignment of the molecular ion to the m/e 418 peak (i.e. M+ 2) arose largely through the absence at that time of mass-marking facilities and the large interval between M˙⁺ and the highest mass fragment ion. Similar hypoiodite reaction of 2-ethyl-(1b) and of 2-phenyl-adamantan-2-ol (1c) gave, respectively, the products (5a) and (7b), the latter arising from the hydrolysis during isolation of the iodo-ether (6c). Investigation of the chemistry of (5b) and (7b) has revealed useful preparative routes to substituted 4-oxahomo- and 2-oxa-adamantanes as well as 7-substituted-bicyclo[3.3.1]nonan-3-ols. Several unusual reactions have been discovered, and reaction mechanisms are suggested.