Borane reaction with 3-hexyne

The stereoselective synthesis of the title compounds has been achieved. Thexylborane on reaction with 2 molar equivalents of 1-iodo-l-alkyne at 0 °C proceeds to near completion (88% for 1-iodo-l-hexyne) to form fully substituted organoborane (33), which upon treatment with 2 molar equivalents of sodium methoxide at 0 °C readily produces frunx-1,2,3-butatrienes (Eq. 102) The same reaction, however, with either 1-chloro or 1-bromo-l-alkynes is sluggish to form the thexyl-l-halo-l-alkenyl-borane . 

Borane adds readily to an internal alkyne as illustrated by its reaction with 3-hexyne. 

Dinuclear palladium complexes catalyze m-hydroarylation of alkynes with arenes.56 The reaction of 3-hexyne with benzene in the presence of a dinulear palladium complex Pd2R2(M-OH)(//-dpfam) [dpfam = j/V,Ar -bis[2-(diphenyl-phosphino)phenyl]formamidinate, R=/>-Tol] and tri(/z-butyl)borane at 100 °C for 4h affords ( )-3-phenyl-3-hexene quantitatively (Equation (53)). The hydroarylation of 3-hexyne with monosubstituted benzenes ( )-3-aryl-3-hexenes with a 2 1 ratio of the meta- and ra -isomers. This regioselectivity is different from that of the hydroarylation of diphenylacetylene catalyzed by Rh4(GO)12.57... 

Hydroboration-iodination of aUtynes. Olefinic side chains can be introduced stercosclcctivcly into cyclic systems by hydroboration-iodination of alkynes. Thus the reaction of l-hexyne with bis(/ru/is-2-methylcyclohcxyl)borane (1) gives the vinyl-borane (2). Treatment of (2) successively with 6 N sodium hydroxide and a solution of iodine in THI yields rrans-l-methyl-2-(cM-l-hexenyl)cyclohexane (3) in 85% yield. Migration of the 2-methylcyclohexyl group thus occurs with retention of configuration. 

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