Positional selectivity of the methylation of 5-substituted tetrazolate anions

The methylation of a series of 15 sodium 5-substituted tetrazolates using iodomethane in acetone/water (4 : 1) has been studied. The reaction yields both 1- and 2-methyl products, and the ratio of these products is discussed in terms of the nature of the 5-substituent. Electronic and steric effects dominate the reaction pathway; both increased substituent electro negativity and steric bulk lead to predominant methylation at N2. Sodium 5-ethoxycarbonyltetrazolate (3n) goes against this trend and an intermediate is proposed where the incoming electrophile is associated with the ester carbonyl group.