Enantioselective Synthesis of Organosulfur Compounds via [2,3] Rearrangements of Ylides Derived from Di(allyl) and Di(propargyl) Sulfide Complexes. Control of Carbon Configuration by an Easily Resolved and Recycled Chiral Transition Metal Auxiliary
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The di(allyl) sulfide complexes [(η5-C5H5)Re(NO)(PPh3)(S(CH2CR=CR′2)2)]+TfO– (4+TfO–; R/R’ = a, H/H; b, CH3/H; c, H/CH3) and t-BuOK (THF, –80 °C) give thiolates (η5-C5H5)Re(NO)(PPh3)(SCH(CR′2CR=CH2)-CR=CR′2) (5a–c, 95–90%) as 93:7, 98:2, and 93:7 mixtures of SS,RR/SR,RS Re,SC diastereomers. Pure enantiomers (S)-4a–c+BF4– give 5a–c as 93:7, ≥99.3:0.7, and 97:3 SS/SR mixtures (85–79%). Reactions with MeOTf yield [(η5-C5H5)Re(NO)(PPh3)(S(Me)CH(CR′2CR=CH2)CR=CR′2)]+TfO– (95–89%), which are treated with EuN+CN– to give MeSCH(CR′2CR=CH2)CR=CR′2(8a–c, 67–58%; 92:8, >99:<1, 96:4 S/R from (S)-4a–c+BF4–) and (η5-C5H5)Re(NO)(PPh3)(CN) (9, 93–78%; >98% ee). Complex (S)-9 can be recycled to (S)-4a–c+BF4–in 2–3 steps. Analogous sequences with 5a,b and PhCH2 I give [(η5-C5H5)Re(NO)(PPh3)(S(CH2Ph)CH(CR′2CR=CH2)CR=CR′2)]+I– (97–79%) and PhCH2SCH(CR′2CR=CH2)CR=CR′2 (11a,b, 82–77%; 93:7, >99:<1 S/R from (s)-4a,b+BF4–). Similar S(CH2C≡CCH3)2 (d) and S(CH2CH=CHR)2 (E; R = e, CH3; f, C(CH3)3; g, C6H5) complexes give thiolates 5d–g as comparable Re,SC diastereomer mixtures. However, 5e–g contain new SCC stereocenters, and only 5f gives high selectivity (89:11). The pentamethylcyclopenladienyl complex 4a-Me5+TfO– yields 5a-Me5 of opposite stereochemistry (7:93 SS,RR/SR,RS). Crystal structures of (S)-4a+SbF6- (triclinic, a 9.800(2), b 10.516(2), c 16.152(3), α 93.20(2), β 107.16(2), γ 81.57(2), (SS)-5a (monoclinic, a 9.881(2), b 12.483(3), c 10.877(2), β 100.23(2)), (SRR,RSS)-5f (triclinic, a 9.578(3), b 14.019(5), c 15.999(4), α 93.22(3), β 97.83(3), γ 107.63(3)), and (SR,RS)-%a-Me5 (monoclinic, a 8.780(2), b 17.379(4), c 20.801(3), β 92.49(2)) establish the configurations given above. The mechanism of diastereoselection is analyzed in detail. © 1995, American Chemical Society. All rights reserved.
author list (cited authors)
Cagle, P. C., Meyer, O., Weickhardt, K., Arif, A. M., & Gladysz, J. A.