Recently we have found new reagents of [(MeO)_3 B-R] Li (1), which, in the presence of the nickel catalyst, react with coupling with allylic acetates and carbonates. These reagents are high reactive so that secondary allylic substrates can be involved as the substrates in the coupling.
First, we applied these reagents to synthesis of brefeldin A.The key intermediate is successfully prepared from 4-cyclopentene-1,3-diol mono acetate (2) and [(2-furyl) -B (OMe)_3] Li (1a) in good yield with high regio- and stereoselectivities. Since reaction of mono acetate 2 using classical coupling reagents are reported to give a mixture of regioisomers, the present success opens a new possibility using the mono acetate 2 as the starting compound. During the synthesis, new conditions of furan oxidation to furnish trans 4-oxo-2-alkenals was found and applied to synthesis of patulolide A and pyrenophorin.
Next, we have developed new reagents [R-B (Me) (-OCH (Me) -CH (Me) O-] Li (3), which are more reactive than [(MeO)_3B-R] Li (1) in the allylic coupling. In addition, the new reagents were found for the first time to be participated in the coupling with aryl mesylates and sterically hindered cis 1-bromo-1-alken-3-ol derivatives, both of which are previously unreactive toward the coupling reaction.