ASYMMETRIC DIELS-ALDER REACTIONS OF CHIRAL (E)-2-CYANOCINNAMATES .2. SYNTHESIS OF THE 4 1-AMINO-2-PHENYL-1-CYCLOHEXANECARBOXYLIC ACIDS IN ENANTIOMERICALLY PURE FORM

High and complementary diastereoselectivities were obtained in the asymmetric Diels-Alder reactions of chiral (E)-2-cyanocinnamates with butadiene when (S)-ethyl lactate and (R)-pantolactone were used as chiral auxiliaries in the presence of TiCl4. The most selective reactions allowed the synthesis of the cycloadducts 2a and 3b, whose absolute configurations were assigned by an X-ray diffraction study of diastereoisomer 3b. The hydrolysis and subsequent hydrogenation of the stereoisomers gave the corresponding enantiomeric cyanocarboxylic acids. From these products the four 1-amino-2-phenyl-1-cyclohexanecarboxylic acids were synthesized in enantiomerically pure form following a protocol with stereocontrolled and stereodivergent transformations.