ENANTIOSELECTIVE SYNTHESES 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 [(5-C5H5)Re(NO)(PPh3)(S(CH2CR=CR2)2)]+TfO (4+TfO; R/R = a, H/H; b, CH3/H; c, H/CH3) and t-BuOK (THF, 80 C) give thiolates (5-C5H5)Re(NO)(PPh3)(SCH(CR2CR=CH2)-CR=CR2) (5ac, 9590%) as 93:7, 98:2, and 93:7 mixtures of SS,RR/SR,RS Re,SC diastereomers. Pure enantiomers (S)-4ac+BF4 give 5ac as 93:7, 99.3:0.7, and 97:3 SS/SR mixtures (8579%). Reactions with MeOTf yield [(5-C5H5)Re(NO)(PPh3)(S(Me)CH(CR2CR=CH2)CR=CR2)]+TfO (9589%), which are treated with EuN+CN to give MeSCH(CR2CR=CH2)CR=CR2(8ac, 6758%; 92:8, >99:<1, 96:4 S/R from (S)-4ac+BF4) and (5-C5H5)Re(NO)(PPh3)(CN) (9, 9378%; >98% ee). Complex (S)-9 can be recycled to (S)-4ac+BF4in 23 steps. Analogous sequences with 5a,b and PhCH2 I give [(5-C5H5)Re(NO)(PPh3)(S(CH2Ph)CH(CR2CR=CH2)CR=CR2)]+I (9779%) and PhCH2SCH(CR2CR=CH2)CR=CR2 (11a,b, 8277%; 93:7, >99:<1 S/R from (s)-4a,b+BF4). Similar S(CH2CCCH3)2 (d) and S(CH2CH=CHR)2 (E; R = e, CH3; f, C(CH3)3; g, C6H5) complexes give thiolates 5dg as comparable Re,SC diastereomer mixtures. However, 5eg 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), 93.20(2), 107.16(2), 81.57(2), (SS)-5a (monoclinic, a 9.881(2), b 12.483(3), c 10.877(2), 100.23(2)), (SRR,RSS)-5f (triclinic, a 9.578(3), b 14.019(5), c 15.999(4), 93.22(3), 97.83(3), 107.63(3)), and (SR,RS)-%a-Me5 (monoclinic, a 8.780(2), b 17.379(4), c 20.801(3), 92.49(2)) establish the configurations given above. The mechanism of diastereoselection is analyzed in detail. 1995, American Chemical Society. All rights reserved.
