CATIONIC RHENIUM DMSO COMPLEX TO AN YLIDE AND SUBSEQUENT [1,2] MIGRATION OF RHENIUM FROM SULFUR TO CARBON A NEW REACTION OF COORDINATED SULFOXIDES - FACILE AND HIGHLY DIASTEREOSELECTIVE DEPROTONATION OF A CHIRAL

Reaction of the chiral, cationic sulfur-ligated DMSO complex [(5-C5H5)Re(NO)(PPh3)- (S(O)(CH3)2)]+BF4-and t-BuO-K+ (CH2Cl2, -80 C) gives the neutral alkyl complex (5-C5H5)Re(NO)(PPh3)(CH2S(O)CH3) (2) in 96% yield as a 99:1 mixture of SR,RS/SS,RR Re,S configurational diastereomers. An intermediate ylide with a ReS(O)(CH3)(CH2-) linkage is proposed. Subsequent [1,2] migration of rhenium from sulfur to carbon then gives 2. In CDCl3at room temperature, 2 slowly equilibrates to a 4:96 SR,RS/SS,RR mixture. A mechanism involving epimerization at sulfur and the methylidene complex [(5-C5H5)Re-(NO)(PPh3)(=CH2)]+X- (4+X-) is supported by (1) enhanced rates in the presence of catalytic amounts of HOTf, which presumably convert the -S(O)CH3moieties to better leaving groups, HOSCH3, (2) reduced rates in the presence of pyridine, and (3) trapping of 4+X- with P(p-tol)3. The crystal structure of (SS,RR)-2 is determined, and possible origins of the kinetic and thermodynamic selectivities are discussed. 1995, American Chemical Society. All rights reserved.

A NEW REACTION OF COORDINATED SULFOXIDES - FACILE AND HIGHLY DIASTEREOSELECTIVE DEPROTONATION OF A CHIRAL, CATIONIC RHENIUM DMSO COMPLEX TO AN YLIDE AND SUBSEQUENT [1,2] MIGRATION OF RHENIUM FROM SULFUR TO CARBON Academic Article