Formation of homoallyl alcohols and 4-chlorotetrahydropyrans from allyl-stannanes, aldehydes and TiCl4 or Cp2TiCl2

Article abstract of DOI:10.1016/0022-328X(90)85055-4

Reaction between Bu3SnCHR¹CH=CHR² (1; R¹ = H, R² = H or Me; R¹, R² = (CH2)3) and EtCHO in the presence of TiCl4 or Cp2TiCl2 are reported.The compound, Cp2TiCl2, has been found to be an effective Lewis acid catalyst for the allylation of EtCHO using 1 (R¹ = H, R² = Me) and 1 (R¹, R² = (CH2)3) in CH2Cl2 or Et2O solutions at -78 deg C; the products after hydrolysis are homoallyl alcohols with stereo- and regio-selectivities different from those found for TiCl4^- reactions.Reactions with an excess of EtCHO in the presence of TiCl4 give 4-Cl-3-R¹-5-R²-2,6-2Et-tetrahydropyrans (2) via insertions of a second EtCHO into the metal-O bond of the initially produced homoallyl alcoholate: the trans-2 compounds are obtained from threo-EtCH(OM')CHR²CH=CHR¹ and cis-2 from erythro-EtCH(OM')CHR²CH=CHR¹ (e.g., M' = TiCl3).