HYDROBORATION OF ALKYNES WITH DICHLOROBORANE-DIMETHYL SULFIDE——SYNTHESES AND SPECTROSCOPIC CHARACTERISTICS OF gem-DIBORON AND ALKENYLBORON COMPOUNDS

The reactions of alkynes with dichloroborane-dimethyl sulfide (HBCl_2·SMe_2) in the presence of boron trichtoride in pentane have been investigated.Both internal and terminal alkynes react with HBCl_2·SMe_2 in the molar ratio 1:2 at 0℃ to give dihydroborating products, gem-bis (dichloroboryl)alkanes, in good yield. Since the dihydroboration of alkynes is suppressed considerably at lower temperature, the internal alkynes and HBCl_2·SMe_2 react quantitatively in the molar ratio 1.4:1 at-20℃ or -30℃ to give the expected alkenyldichloroboranes.Under the same conditions,the terminal alkynes, however, undergo both monohydroboration and chloroboration.When terminal alkynes react with boron trichloride in the molar ratio 1 :1.1 in pentane, the chloroborating products, 2-chloro-1-alkenyldichloroboranes have been obtained in high yield.All dichloroboranes are readily converted by alcoholysis into the corresponding boronic esters.The resulting compounds have been characterized by IR, ~1H,~(11)B, and ~(13)C N