Betylates. 2. The formation and high reactivity of alkyl [0]betylates

Abstract

Unhindered primary alkyl N,N-dimethylsulfamates (1) react with methyl fluorosulfate to give the corresponding alkyl fluorosulfates (3) and the betaine, [Formula: see text] (4), evidently by way of the intermediate alkyl [0]betylate fluorosulfate (2); with certain other alkyl esters (1) products of substitution, elimination, and rearrangement are formed. The reaction not only provides a potentially useful route to simple alkyl fluorosulfates, but serves to demonstrate the powerful nucleofugality of the [0]betylate group. To obtain a method for predicting the reactivity of [0]betylates, we have compared substituent parameters with rate constants in four series of nucleophilic displacements involving esters of the general structure ROSO2Z; correlation (of log k) with σ* is mediocre but a new parameter, [Formula: see text] with a "15% resonance" contribution as defined by Swain and Lupton, gives good to excellent agreement in the four reaction series. Evidence is presented for formation of the 7-norbornyl cation via the [0]betylate from 7-norbornyl N,N-dimethylsulfamate and methyl fluorosulfate. Comparison with what is known of the reactivities of 7-norbornyl p-toluenesulfonate and trifluoromethanesulfonate esters serves to confirm that [0]betylates are among the most nucleofugal functions of which a derivative has been fully characterized.