Diels-Alder reactions diastereoface selective

Asymmetric Diels-Alder reactions. Diels-A Idcr reaction of the acrylate (2) of ethyl (S)-lactate with cyclopentadiene gives four adduas with the usual preference for endo-rather than ejro-addition, which is increased by use ot a Lewis acid catalyst (endo/exo = 12-39 1). The Lewis acid catalyst can also control the diastereoface selectivity of endo-addition but not that of ejco-addition (equation 1) In the noncatalyzed reaction or in the presence of BF, etherate or AlCl, (lS,2S)-3 is lormed in excess. With SnCL or TiCL, (IR,2R)-3 is formed in excess. The stereoselectivity can be increased and polymerization decreased by addition of n-hexane. The adducts (3i can be hydrolyzed with LiOH in THF/ H,0 at 20° without epimerization. 

Asymmetric Diels-Alder reactions. Chiral a,p-unsaturated N-acyl oxazolidones exhibit high diastereoface selection in Diels-Alder reactions, particularly those conducted in the presence of diethylaluminum chloride (1.2 equiv.). 

DIASTEREOFACE-SELECTIVE DIELS-ALDER REACTIONS WITHOUT REMOVAL OF THE INDUCING MOIETY... 

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