Synthesis of Propionate Motifs: Diastereoselective Tandem Reactions Involving Anionic and Free Radical Based Processes
作者:Yvan Guindon、Karine Houde、Michel Prévost、Benoit Cardinal-David、Serge R. Landry、Benoit Daoust、Mohammed Bencheqroun、Brigitte Guérin
DOI:10.1021/ja010805m
日期:2001.9.1
employing a Mukaiyama reaction in tandem with a hydrogen transfer reaction for the elaboration of propionate motifs. The nature of the protecting groups on the chiral β-alkoxy aldehyde and the type of Lewis acid used are varied to modulate the stereochemical outcome of the tandemreactions. The mode of complexation is thus controlled (monodentate or chelate) for the Mukaiyama reaction to give access to
dialkoxyboranes derived from thioesters were found to be stereoconvergent: both Z and E enolates give syn aldol condensation products. The thioester additions to chiral aldehydes were studied. Internal selectivity (syn) was usually very high, while the relative stereoselectivity ranged from poor to good, depending on the specific aldehyde used. The aldol products were transformed to known compounds for correlation
Stereoselection in the reaction of acid halides and vinylogous urethanes
作者:Richard H. Schlessinger、James R. Tata、James P. Springer
DOI:10.1016/s0040-4039(00)96744-3
日期:1987.1
Acidhalides which carry either an α-phenyl or α-alkoxy residue show fascinatingly high and useful diastereoselection on condensation with the vinylogous urethane derived ketene acetal enamine 3. Optically active halides of this type undergo reaction with 3 accompanied by very high diastereofacial selectivity.
The antipodal form 2 of the tetraene fragment, the C1 – C12 portion, of calyculins (1) has been synthesized by use of the stereoselective hydrogenation of the butenolide 6 followed by the successive Wittig-type chain elongation of the lactol 9 as key steps.