Access to Central Carbon Chirality through Cycloplatination of 1-(2-Pyridinylthio)propanone by <i>cis</i>-[PtCl₂(<i>S</i>-SOMe(<i>p</i>-tolyl))]. The Crystal Structure of (<i>S</i>_s<i>S</i>_c)-[Pt{py{SCHC(O)Me}-2}Cl(SOMe(<i>p</i>-tolyl))]

Abstract

Cycloplatination of the prochiral sp3 C−H bond of 1-(2-pyridinylthio)propanone (py{SCH2C(O)Me}-2, 1a) by cis-[PtCl2(SOMe2)] in dry ethanol affords [Pt{py{SCHC(O)Me}-2}Cl(SOMe2)] (3a) in 77% isolated yield without any side product. The same reaction using the chiral complex cis-[PtCl2(S-SOMe(p-tolyl))] (the absolute configuration of sulfur is indicated for the coordinated ligand) leads to two cycloplatinated diastereoisomers, 4a (SsRc) and 4b (SsSc), in 12.9 and 33.7% yield, respectively (de 44.6%). Their absolute configuration was deduced from the analysis of the 1H NMR spectra and confirmed by an X-ray structural investigation of 4b. Diastereomer 4b was shown to react with PPh3 to give the enantiomer [Pt{py{SCHC(O)Me}-2}Cl(PPh3)] with the central carbon chirality only. Rather surprisingly, attempted cycloplatination of py{SCH2C(O)Ph}-2 (1b) by cis-[PtCl2(SOMe2)] affords the cycloplatinated complex [Pt{py{SCHC(O)Ph}-2}Cl(SOMe2)] (3b) in a miserable yield.