The asymmetric Horner-Wadsworth-Emmons (HWE) reaction of the prochiral ketones 8alb with the phosphonoacetates 10a, ent-lOa, 10b and rac-16, which contain 8-phenylmenthol, 8-phenylnormenthol and fran~-2-(triphenylsilyl)cyclohexanol, respectively, as chiral auxiliaries, were studied. The HWE reaction of 8a with the phosphonoenolates Li-10aIb at low temperatures gave the esters 7alb and llalb in high yields with diastereoselectivities up to 97:3. The ( E )configured esters 7a/b serve as starting material for the total synthesis of (+)-3-oxacarbacyclin. Similarly, the reaction of 8b with ent-Li-l0a gave the esters ent-7b and ent-llb in a ratio of 95:5 in 82% yield. The olefination of 8b with rac-16 afforded a mixture of the esters rac-17 and rac-18, of yet unassigned configuration, in a ratio of 70:30. The HWE reactions of 8alb with Li-lOa, ent-Li-l0a and rac-Li-lob show linear temperature-diastereoselectivity relationships. The stereochemical course of the HWE reactions can be under-stood in terms of a selective addition of the chiral (E)-configured phosphonoenolate from its least hindered side to the ketone 8 at the convex side. The asymmetric Peterson reaction of 8b with the silyl enolate Li-20 gave the esters ent-irb and ent-llb in a ratio of 89:ll. The diastereomerically pure phydroxy esters 22, rac-25 and 27, which contain 8-phenylmenthol, trans-2-(triphenylsilyl)cyclohexanol and 3-([(3,5dimethylphenyl)phenylsulfonyl]amino]isoborneol, respectively, as chiral auxiliaries, were prepared by a highly selective addition of the enolates Li-21, rac-Li-24 and Li-26 to the ketone 8b. The asymmetric Martin dehydration of 22, rac-25 and 27 with the sulfurane 23 proceeds with stereoselectivities ranging from 82: 18 to 99: 1. Interestingly, the HWE, Peterson and Martin reactions involving 8-phenylmenthol as the chiral auxiliary all proceed with the same sense of asymmetric induction.
Reaction of the optically active bissiloxy bismesylate (I) with the α‐lithiated sulfone (II) produces the bicyclic system (III) which is then hydrolyzed, forming the ketone (V).
Total Synthesis of (+)-3-Oxacarbacyclin. Part 1. Retrosynthesis and Asymmetric Olefination Through Horner-Wadsworth-Emmons, Peterson and Martin Reactions.-The Horner-Wadsworth-Emmons reaction of the ketones (I) and (V) with the phosphonates (II), (VI), and (IXb), the Peterson reaction of (V) with the silicon compound (IXa), and the Martin reaction to the esters (XIV) and (XV) are studied intensively, because they can be used as key step in the total synthesis of (+)-3-oxacarbacyclin. The stereochemistry can be explained by a high substrate and auxiliary-induced facial selectivity. Interestingly, all reactions involving 8-phenylmenthol as chiral auxiliary proceed with the same asymmetric induction.-(GAIS, H.-J.; SCHMIEDL, G.; OSSENKAMP, R. K. L.; Liebigs Ann./Recl. (1997) 12,
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