Comparison of the allylation reactions of aldehydes using allylstannanes with boron trifluoride etherate and boron trichloride

Article abstract of DOI:10.1016/0022-328X(90)85025-T

Reactions between allylstannanes, R²CH=CHCHR¹SnBu3 (R¹ = R² = H (4); R¹ = H, R² = Me (5); R¹R² = (CH2)3 (6) and aldehydes, RCHO (e.g.R = Et) in the presence of BF3<*>OEt2 in CH2Cl2 at -78 deg C produce stereoselectively erythro-RCH(OH)CHR²CH=CHR¹ (with one equivalent RCHO) and 4-OH-3-R¹-5-R²-2,6-R2-tetrahydropyrans (with an excess of RCHO).In contrast, when BCl3 is used in place of BF3<*>OEt2 the reactions give mixtures of chlorinated alkenes (both homoallyl chlorides and allyl chlorides) and 4-Cl-3-R¹-5-R²-2,6-R2-tetrahydropyrans (3; X = Cl).Thus 5, EtCHO and BCl3 (all equimolar) provide EtCHClCH2CH=CHMe (51percent, (E) + (Z)), EtCHClCHMeCH=CH2 (7percent, erythro + threo), EtCH2CH=CH-CHMeCl (30percent, (E) + (Z)) and 3 (12percent, X = Cl); with EtCHO (2.2 equivalents). 3 (X = Cl; cis/trans = 70/30) becomes the sole product.The product, erythro-EtCHClCHCH=CH(CH2)2CH2 (97percent) was produced from equimolar EtCHO, BCl3 and 6; with excess EtCHO (2.2 equivalents), 9-Cl-2,4-Et2-cis-3-oxabicyclo<3.3.1>nonane (17percent; cis/trans = 45/55) and erythro-EtCHClCHCH=CH(CH2)2CH2 (78percent) were obtained.