Modular pyridine-type P,N-ligands derived from monoterpenes: application in asymmetric Heck addition

Novel (diphenylphosphinophenyl)pyridine ligands (+)-8, (+)-15, (-)-21, and (-)-26 were synthesized from (-)-beta -pinene, (+)-3-carene, (+)-2-carene, and (-)-alpha -pinene, respectively, via Krohnke annulation as the key step , and shown to effect less than or equal to 88% ee in Heck addition (27 --> 28). Ligands (+)-15 and (-)-21 are quasi-enantiomeric; ligands 8 and 26 ca n be prepared in both enantiomeric forms from (+)- and (-)-enantiomers of a lpha- and beta -pinene, respectively. (C) 2001 Elsevier Science Ltd. All ri ghts reserved.