Cyclopropylcarbinyl–oxocarbonium ions. Part VII. Orientational effects

Abstract

The anomeric 2,3-dideoxy-2,3-C-methylene-D-allopyranosides (2α and β) along the with homoallyl iodide (6) comprise a configurationally related cyclopropylcarbinyl–system; the 2,3-dideoxy-2,3-C-methylene-D-mannopyranosides (7α and β) along with the homoallyl iodide (11) comprise a second, different system. The three members of each system should undergo solvolysis through a common, highly stabilised cyclopropylcarbinyl–oxocarbonium ion [(3) or (8), respectively]. Evidence in support of this is the fact that compounds (2α and β) and (6) are hydrolysed to the same δ-hydroxy-cyclopropanecarbaldehyde (5), presumably formed via the related, cyclic hemiacetal (4). A study of the solvolysis of the cyclopropyl compounds (2α and β) and (7α and β) indicates that orientational effects are not important; however, in the case of the homoallyl iodides (6) and (11) an effect is observed.