TI-IV-BINOLATE-CATALYZED HIGHLY ENANTIOSELECTIVE ADDITIONS OF BETA-SUBSTITUTED ALLYLSTANNANES TO ALDEHYDES

Enantiomerically pure homoallyl alcohols were prepared from aldehydes R(1)-CH=O (R(1)=Ph, pentyl, Ph-CH=CH-, iPr) and beta-substituted allyl stannanes H2C=CR(2)-CH2-SnBu(3) (R(2)=pentyl, tBuPh(2)SiO-CH2-, tBuPh( 2)SiO-CH2-CH2-, PhS-CH2-CH2-). These reactions were catalyzed by the s ame additives-Ti(OR)(4) (10 mol%) and (R)BINOL (20 mol%)-that Keck et al. used in analogous reactions with methallyl-and allyltributylstanna ne. To attain optimum ee values (96.4-99.2% in the reaction with hexan al) these additives had to be premixed for 2 h at room temperature. Ti (OEt)(4) and Ti(OiPr)(4) gave equally good results, while Ti(OMe)(4), Ti(OCHEt(2))(4), and Ti(OtBu)(4) were inferior. Our proce dure works i n the absence of molecular sieves [which were previously found to give rather unreliable results in reactions catalyzed by Ti(OiPr)(4)/(R)-B INOL] and can be extended to enantioselective addition reactions with allyl- and methallyltributylstannane, too (+hexanal: 97.4 and 97.0% ee , respectively).