Stereochemistry alkenylmetals

B.iv.c. trans-a,pSubstituted Alkenylmetals. The accessibility of trani-a,/3-substituted alkenyhnetals is still rather limited, and only a few examples of this type of crosscoupling reactions have been reported (Table 6). Notably, trtmi-a,/3-substituted alkenylboronates can be prepared by hydroboration of 1-bromo-l-alkynes followed by subsequent treatments with organolithiums and bases, a procedure similar to that for the preparation of (Z)-/3-substituted alkenylboron compounds.t " Et The Pd-catalyzed crosscoupling reaction of the resultant organoboranes with aryl halides proceeds with complete retention of alkenyl stereochemistry to give trisubstituted alkenesP (Scheme 33). 

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