Iminodienophiles

Diels-Alder reactions of enantiomerically enriched 2H-azirine 3-phosphon-ates (281), a new class of chiral iminodienophiles, and dienes stereoselectively furnish optically pure, bicyclic aziridine adducts (282). Hydrogenation of (282) results in a ring opening that affords the first examples of optically pure quaternary piperidine phosphonates. Two step synthesis of an enantiomeric pure cyclic phosphite (283) and its application as a chiral phosphorus nucleophile in the asymmetric Michael addition to nitroalkenes (284) provides an efficient... 

Boron Lewis acids have also been found to be very useful in Diels-Alder reactions that employ chiral substrates. Anderson and coworkers have shown that using a combination of Bp3 OEt2 and trifluoroacetic acid, it is possible to obtain the cycloaddition products of nonactivated iminodienophiles such as (16) in good yields and high diastereoselectivity (Equation 11) [17]. 

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