Diallyl sulfide complexes of chiral iron and ruthenium Lewis acids: Ylide generation and diastereoselective [2,3] sigmatropic rearrangements to give thiolate complexes with new carbon stereocenters
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Reactions of the racemic iron diallyl sulfide complex [(5-C5H5)Fe(CO)(PPh3)(S(CH 2-CH=CH2)2)]+BF4- and t-BuOK (CH2Cl2 or THF, -80 to -60C) give the thiolate complex (5-C5H5)Fe(CO)(PPh 3)(SCH(CH=CH2)CH2CH=CH2) (65-92%) as 77-68:23-32 mixtures of SS,RR/SR,RS Fe,SC diastereomers. Reactions of the enantiomerically pure ruthenium diallyl sulfide complexes [(5-C5H5)Ru(S,S-chiraphos)(S(CH 2CR=CH2)2)]+PF6- (5+PF6-; R = a, H; R = b, CH3) and t-BuOK (CH2Cl2, -98C) give the thiolate complexes (5-C5H5)Ru(S,S-chiraphos)(SCH(CR=CH 2)CH2CR=CH2) as 78:22 (8a, >99%) and 87:13 (8b, 97%) mixtures of chromatographically separable SSS/SSR PC,PC,SC diastereomers. These transformations likely involve intermediate sulfur ylides as described in the title. Reactions of 8a,b with CH3I or PhCH2I and then NaI (acetone, reflux) give, via cationic methyl or benzyl sulfide complexes, enantiomerically enriched RSCH(CH2CR=CH2)CR=CH2 (R/R = H/CH3, 75%; CH3/CH3, 71%; H/PhCH2 and CH3/PhCH2, >99%) and (5-C5H5)Ru(S,S-chiraphos)(I) (6, 97%). Complex 6 is readily recycled to enantiomerically pure 5a,b+PF6- (NH4+PF6-, CH3OH, S(CH2CR=CH2)2; 94-97%).
