1.2- silylboration

I 7 Hydroboration, Diboration, Silylboration and Stannylboration Tab. 1-3 Isomerization to the Terminal Carbon 1. HBX2/catalyst... 

The palladium-catalyzed stannylboration (90) [124] or silylboration (87) [109, 114] succeeds in the intramolecular carbocyclization of diynes and enynes (Scheme 1-27). It is interesting that a very strained four-membered cycUzation of hexa-l,5-diyne proceeds without any difficulties, similarly to five- or six-membered cycUzation. The boryl group is selectively introduced into the more reactive C=CH rather than C=C for enynes and into the terminal C=CH rather than the internal C=CR for diynes, again suggesting a mechanism proceeding through the first insertion into the Pd-B bond in preference to the Pd-Sn or Pd-Si bond. 

Miyaura, N. Hydroboration, Diboration, Silylboration and Stannylboration. In Catalytic Heterofunctionalization-, Togni, A., Griitzmacher, H., Eds. Wiley-VCH Weinheim 2001 pp 1-47. 

Like alkenes, alkynes do not react readily with trialkylboranes. Under severe reaction conditions, only hydroboration products are obtained.116 Mikhailov113 showed that triallylboranes react with various alkynes (20 C) to afford syn addition products of type (78) which rapidly cyclize (40-60 C) to give the cyclic boranes of type (79 Scheme 42). In the case of trimethylsilylacetylene and ethoxyacetylene, the reaction affords compounds of type (78 R = MesSi or OEt) which do not cyclize further.113 Recently, a transition metal silylboration reaction has been described by Oshima and cowoikers.117 A formal syn carboboration reaction leading to a variety of alkenylboranes has been reported by Suzuki and cowoikers118 (Scheme 43). Hexamethyldistannylacetylene (80) reacts readily with various trialkylboranes119 to afford syn addition products of type (81 equation 25). 

The reactivity of l-silyl-l-boryl-2-alkenes 68 obtained by gem-silylboration of allyl-chloride were studied by Hiyama et al. [36]. Allylsilanes 68, engaged in SMS reactions, afford the desired trans-vinylboranes 69 with good yields (Scheme 13.29). 

Internal acetylenes, Ni-mediated reactions, 10, 546 Internal alkenes, ethylene co-polymers, 4, 1145 Internal alkynes in alder-ene reaction, 10, 567 intermolecular hydrosilylation with ruthenium, 10, 802 with yttrium, 10, 801 silylboration, 9, 163 silylformylation, 11, 483... 

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