Hydroboration and haloboration of propyne and 1-butyne

Hydroboration of propyne and 1-butyne with HBCl 2 obtained from BCl 3 and Me 3 SiH in equimolar amounts leads to 1,1-bis(dichloroboryl)alkanes 1. When BCl 3 is used in excess, no 1,1-bis(dichloroboryl)alkanes 1 but E-1-dichloroborylalkene 2 besides E-1-dichloroboryl-2-chloro-alk-1-ene 3 are formed. Other by-products are tris(2-chloro-alk-1-ene-1-yl)borane 4 and bis(2-chloro-alk-1-ene-1-yl)chloroborane 5. The reaction of 3 with catechol and the formation of pyridine adducts of 4 and 5 lead to crystalline products. The composition of the products was determined by NMR spectroscopy, MS spectrometry and X-ray structure analyses of 6a, 6b, 7a and 8b.