Chiral allenes are readily accessed in a single pot operation in the reaction of terminal alkynes, aldehydes, chiral secondary amines, and zinc halides in good yields (up to 77% yield) and excellent enantioselectivities (up to 99% ee) in toluene at 120 °C. The reaction proceeds through initial formation of chiral propargylamine intermediates with creation of a new stereogenic center and subsequent chirality transfer via an intramolecular hydride shift to produce chiral allenes with high enantiomeric purities.
D-(-)-Camphorquinone imines prepared using methanolic ammonia, ethanol amine, exo-(-)-bornylamine, ethylene diamine, propylene diamine, and trans-(R,R)-1,2-diaminocyclohexane, upon reduction using sodium borohydride in methanol, give the corresponding chiral exo amino alcohol and diamine derivatives in good yields (75-95%).
Simple, convenient methods have been developed using readily available, easy-to-handle reagents to access a variety of chiral amino alcohols and amines, which have considerable potential for applications in asymmetric organic transformations. Scholars from this laboratory in India have made significant contributions to this field, which is the subject of the current review.
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