Kinetics and mechanism of the C-S coupling reactions of aryl Grignard reagents with aryl arenesulfonates

Abstract

Abstract:The kinetics of the C-S coupling of arylmagnesium bromides with phenyl tosylate has been studied in THF: toluene at 90°C. The reaction is first order in Grignard reagent and first order in phenyl tosylate. Kinetic data, Hammett relationship and activation parameters are consistent with a nucleophilic addition mechanism involving rate determining attack of carbanion to sulfonyl group followed by a fast phenoxide group leaving.© Versita Warsaw and Springer-Verlag Berlin Heidelberg.

Sulfonyl transfer mechanism in C–S coupling of phenylmagnesium bromide with phenyl arenesulfonates

“…In order to gain some insight into the mechanism of thiophilic attack of carbon nucleophiles at S on the sulfonates, we have undertaken a detailed kinetic and mechanistic study [34]. We proposed a mechanism for C-S coupling of aryl Grignard reagents with aryl arenesulfonates, which is consistent with kinetic data, activation parameters and Hammett relationship for the substituent effects of aryl nucleophile.…”

“…We have already discussed the kinetics of phenylmagnesium bromide 1a with phenyl tosylate 2a in THF:toluene (7:10) at 60°C [34]. The reaction obeys clean second order kinetics:…”

An insight into the C–S coupling mechanism of aryl Grignard reagents with aryl arenesulfonates

“…For the sulfonate addition of aryl Grignard reagents, transition state TS 2 as having well advanced C-S bond formation with minimal S-OR 2 bond breakage was proposed [34,35]. However, partial transfer of R to the sulfonyl moiety in the early transition state TS 1 may lead to the formation of Scheme 3 Proposed mechanism for C-S coupling of aryl Grignard reagents with aryl arenesulfonates transition state TS 2 which is stabilized due to chelation of Mg by oxygen atoms in the sulfonyl moiety.…”

“…However, the kinetic and mechanistic details of C-S coupling of aryl Grignard reagents with aryl arenesulfonates have been recently reported by Erdik et al [34][35][36]. A stepwise S N a mechanism was offered (Scheme 2).…”

“…Then, a simple rate law can be derived for the sulfonate addition of Grignard reagents in THF:toluene comprising fast equilibrium formation of complex A [44] and rate determining second order [34][35][36] conversion of A to the product intermediate B;…”