Borate boron-copper complex

The ate complex prepared from B-methoxy-9-BBN and Bu3SnLi [24] adds under copper(I)-catalyzed reaction to 1-alkyne to yield exclusively or predominantly lithium [2-tri-n-butylstannyl-(Z)-l-alkenyl]-l-borates [25]. These borates are selectively coupled in the presence of organopalladium or organo-cuprate with a variety of electrophiles (Chart 24.5), exclusively at the vinylcar-bon-boron bond to form a carbon-carbon bond (Table 24.8) [25]. The process is extremely versatile, as various functional groups are tolerated. However, an alkene with opposite regiochemistry (entry K, Table 24.8) [25] is obtained when BF,-Et,0 is added to the initial reaction, which is then refluxed. 

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