Ephedrine Mannich reaction

The oxazaborolo-benzoxazaborininone derivatives 116 of resorcinar-ene were synthesized in 50—75% yields and in 98% de via a Mannich reaction with L-prohne followed by treatment with a boronic acid or ester (Scheme 38) (2003TA2787). Introduction of the electrophilic boron atom into this structure opens up a potential use for the catalysis of asymmetric reactions. The derivatives 116 were determined to exist as either crown or diamond conformers according to ID and 2D NMR experiments. Similar derivatives can also be prepared from (lS,2R)-ephedrine (2004MI75). 

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