Chiral acetals derived from aldehydes and (-)-(2R,4R)-2,4-pentanediol are cleaved selectively by organoaluminumreagents. The reaction proceeds via the retentive-alkylation process with >95% selectivities in most cases. Trialkylaluminum reagent is utilized for higher alkyl transfers, but for smaller alkyl transfers, a newreagent system, combining trialkylaluminum and the halophenols such as pentafluorophenol
Efficient One-Step Aldol-Type Reaction of Ketones with Acetals and Ketals Mediated by Dibutylboron Triflate/Diisopropylethyl Amine
作者:Lian-Sheng Li、Sanjib Das、Subhash C. Sinha
DOI:10.1021/ol030108u
日期:2004.1.1
one-step Mukaiyama aldol-type reaction has been developed for the synthesis of beta-alkoxy carbonyl compounds starting from ketones and acetals/ketals. The reaction is mediated by a combination of Bu(2)BOTf and i-Pr(2)NEt affording the products in high yields. Formation of the two possible diastereoisomers of the beta-alkoxy ketones from the chiral acetals shows that the condensation takes place by an
Boron fluoride promoted cleavage of acetals by organocopper reagents application to asymmetric synthesis
作者:J.F. Normant、A. Alexakis、A. Ghribi、P. Mangeney
DOI:10.1016/0040-4020(89)80078-x
日期:1989.1
BF3. Et2O, organocopper and cuprate reagents promote the substitution of one alkoxy group of an acetal. Under the same conditions, alkoxy tetrahydropyrans react selectively, by ring cleavage. Chiral cyclic acetals, having a C2 axis of symmetry are diastereoselectively cleaved. The method serves to synthesize chiral secondary alcohols, after the removal of the chiral auxiliary.
Regioselectivity in the ring opening of 2-phenyl-1,3-dioxan-2-yl radicals derived from cyclic benzylidene acetals and comparison with deoxygenation of a carbohydrate diol via its cyclic thionocarbonate
作者:Brian P Roberts、Teika M Smits
DOI:10.1016/s0040-4039(01)00540-8
日期:2001.5
Ring-opening β-scission of monocyclic 2-phenyl-1,3-dioxan-2-yl radicals gives preferentially the more stabilised alkyl radical. However, analogous bicyclic radicalsderived from two 4,6-O-benzylidene glucopyranosides afford primary radicals in preference to secondary radicals, a result that can be rationalised with the aid of DFT calculations. The report by Barton and Subramanian, that the opposite