2001 diastereoselective syntheses, enantioselective syntheses

diastereoselective syntheses, enantioselective syntheses (incl. cis/trans-isomerism)O 0031

16 - 034Highly Enantioselective Protonation of the 3,4-Dihydro-2-methylnaphthalen-1(2H)-one Li-Enolate by TADDOLs. — Theenantioselective protonation of the lithium enolate of tetralone (III) is stud-ied employing nine chiral tetraaryl-1,3-dioxolane-4,5-dimethanol (TADDOL)derivatives such as (I) or TDD as proton sources. The Li-enolate is generatedeither from the enol acetate (II) or directly from racemic ketone (III) or from thesilyl enol ether (IV), and is then treated with the TADDOL derivatives. Bestresults with up to 99% e.e. of the (S)-enantiomer are obtained with 1-naphthyl-substituted TADDOL derivatives whereas tetrakis(2-naphthyl)-, tetraphenyl- ortetraphenanthryl-substituted derivatives only give moderate enantioselectivitiesfavoring the S-enantiomer (III). Among the tested TADDOL derivatives, onlyTDD affords the (R)-enantiomer mainly. Non-linear effects in the protonationof the Li-enolate by addition of (Ib) are discussed. — (CUENCA, ANA;MEDIO-SIMON, MERCEDES; ASENSIO AGUILAR, GREGORIO; WEIBEL,DANIEL; BECK, ALBERT K.; SEEBACH, DIETER; Helv. Chim. Acta 83(2000) 12, 3153-3162; Dep. Quim. Org., Univ. Valencia, E-46100 Burjassot,Valencia, Spain; EN)

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