FACILE SYNTHESES OF TICL2(TADDOLATE)(L2), EFFICIENT ASYMMETRIC ETHYLATION OF PHCHO, AND AN UNEXPECTED REARRANGEMENT OF THE TETRAMETHYL ANALOGUE OF THE TADDOL LIGAND

Facile syntheses of TiCl2(TADDOLate)L2 (TADDOL = α,α,α‘,α‘-tetraphenyl-1,3-dioxolane-4,5-dimethanol; L = THF (1), AcOEt (2)) were developed from reactions of TiCl4 with the TADDOL ligand in coordinating solvent L. The labile solvent ligands L can be replaced by a neutral bidentate ligand such as 1,2-bis(diphenylphosphino)ethane (dppe) or 3,3-dimethyl-2,4-pentanedione (diketone) to give TiCl2(TADDOLate)(L2) (L2 = dppe (3), diketone (4)). The molecular structure of complex 3 shows a structure with two chlorides in trans positions, and the dppe ligand is trans to the strong alkoxide ligands. The most significant features of the structure are the long Ti−P(phosphine) bond distances observed, indicating considerable steric hindrance arising from the TADDOLate ligand in the complex. In a reaction of the TADDOL analogue α,α,α‘,α‘-tetramethyl-1,3-dioxolane-4,5-dimethanol with TiCl4 in Et2O, the unexpected complex 6 derived from rearrangement of the chiral diol ligand was obtained. This rearrangement is apparently...