Reactions of t-BuOK and dibenzyl, benzyl allyl, and allyl beta-keto sulfide complexes of the chiral rhenium Lewis acid [(eta(5)-C5H5)Re(NO)(PPh(3))](+): Highly diastereoselective or chemoselective [2,3]-sigmatropic rearrangements

Reaction of the dibenzyl sulfide complex [(eta(5)-C5H5)Re(NO(PPh(3)(S(CH(2)Ph)(2))](+)TfO(-) (4a(+)TfO(-)) and t-BuOK (THF, -80 degrees C) gives the thiolate (eta(5)-C5H5)Re(NO)(PPh(3))(SCH(o-C6H4CH3)Ph) (5a; 99%) as a 96:4 mixture of SR,RS/SS,RR Re:C diastereomers. This transformation involves initial deprotonation of a benzyl group to give an ylide, followed by [2,3]- and [1,3]- rearrangements. A crystal structure of (SR,RS)-5a establishes the configuration. Similar reactions of the benzyl allyl sulfide complexes [(eta(5)-C5H5)Re(NO)(PPh(3))(S(CH(2)CR=CH2)CH2-Ph)](+)TfO(-) (R = H, CH3) give mainly the thiolates (SS,RR)-(eta(5)-C5H5)Re(NO)(PPh(3)(SCH(CH2-CR=CH2)Ph), derived from benzyl group deprotonation. Some thiolates derived from allyl group deprotonation also form. Similar reactions of the allyl beta-keto sulfide complexes [(eta(5)-C(5)R(5))Re(No)(PPh(3))(S(CH(2)CR'=CR ''(2))CH(2)COPh)](+)X(-) (R/R'/R '' = H/H/H, H/H/CH3, H/CH3/H, CH3/H/H) give the thiolates (eta(5)-C(5)R(5))Re(NO)(PPh(3))(SCH(CR''(2)CR'=CH2)COPh), derived from CH(2)COPh group deprotonation, as >96: <4 to 68:32 diastereomer mixtures. Reactions of 4a (+)TfO(-) with MeLi give mainly the [1,2]-rearrangement product (eta(5)-C5H5)Re(NO)(PPh(3))-(SCH(CH(2)Ph)Ph) ((35-70):(65-30) diastereomer mixtures), which has been independently synthesized. The thiolate ligands are easily converted to free methyl sulfides. Mechanisms of diastereoselection, and similar reactions of organic sulfonium salts, are discussed.