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2005
Diastereoselective syntheses
O 0031
p-Menthane-3-carboxaldehyde: A Useful Chiral Auxiliary for the Synthesis of
Quaternary Carbons of High Enantiomeric Purity. — A series of com05- 028 Chiral
pounds bearing a chiral quaternary carbon atom is synthesized by a previously reported
method employing aldehyde (II) as chiral auxiliary. The route proceeds via allylic alcohols which are prepared with high diastereoselectivities from aldehyde (II) and
alanes, generated in situ. To obtain high diastereomeric excesses of alcohols like (VI)
and (XX) (cf. the following paper) having a newly formed (S) stereocenter, a conversion of the (R)-epimers into keto derivatives followed by diastereoselective reduction
using LiBHEt3 is performed. By application of Goering's conditions, consisting of the
addition of monoalkylcyano magnesiocuprates on pivalate esters, regioselective SN2'
attack of the cuprate reagent affords the target compounds with essentially complete
transfer of the chirality. This reaction fails for bulky cuprates (to be continued). —
(SPINO*, C.; GODBOUT, C.; BEAULIEU, C.; HARTER, M.; MWENE-MBEJA, T.
M.; BOISVERT, L.; J. Am. Chem. Soc. 126 (2004) 41, 13312-pp; Dep. Chim., Fac.
Sci., Univ. Sherbrooke, Sherbrooke, Que. J1K 2R1, Can.; Eng.) — Klein
2005
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