DIASTEREOSELECTIVE AND ENANTIOSELECTIVE SYNTHESIS OF ALLENYLCARBINOLSTHROUGH S(E)2' ADDITION OF TRANSIENT NONRACEMIC PROPARGYLIC STANNANESTO ALDEHYDES

The nonracemic allenylstannane 1c was prepared by S(N)2' displacement of mesylate 8 with Bu(3)-SnLi-CuBr . SMe(2). Treatment of this stannan e with BuSnCl(3) followed by addition of isobutyraldehyde at -40 degre es C afforded the syn allenylcarbinol 4c in nearly 80% yield, The nonr acemic aldehydes (S)- and (R)-16 were similarly converted to the adduc ts 17 and 18 in high yield with good to excellent diastereoselectivity . Best results were obtained when hexane was employed as the solvent, A reaction pathway is proposed to account for the steric preference of these additions, The allenylcarbinols were converted stereospecifical ly to the cis-2,5-dihydrofurans 23-25 upon treatment with catalytic Ag NO3 in acetone.