In the reaction of tribromoborane with 1-alkynes,
cis-addition occurred to give [
Z] -2-bromo-1-alkenylboranes. On the other hand, bromoboration reaction of acetylene gave trans-addition product. Both reactions proceeded stereoselectively and (bromoalkenyl) boranes could be obtained with high selectivity. trans-Alkenes, α, β-unsaturated ketones, α, β-unsaturated esters were prepared stereoselectively by the stepwise crosscoupling reaction of the haloboration adducts. As the application, prostaglandin B
1 methyl ester was synthesized. This method was also used for the synthesis of the polyenes which were converted to the polycyclic compounds by the intramolecular Diels-Alder reaction. Bromoboration reaction of allene provided (2-bromoallyl) borane and the reaction of (2-bromoallyl) borane with carbonyl compounds was also described.
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