From organoboranes 2+2 type

Organoborates are readily prepared from various types of organoboranes. 

Table 1. Thermal rearrangement of organoboranes resulting from the hydroboration of tetrasubstituted cyclopentene derivatives of type 34.

This type of bonding can be observed by X-ray crystallography in the initial products from the reaction of dialkyldialkynyltin compounds with organoboranes (equation 8-53).64 The ethyne group is unsymmetrically bonded to the tin with C-Sn distances 233.9(4) and 252.3(5) pm, and the other three groups about the tin are close to coplanar, as would be expected for a triorganotin cation. 

Oxidations of organoboranes involve numerous reagents and several different general ntechanisms, most of which parallel those which occur for other types of organoborane reactions. The mechanisms fall under three broad headings (i) ionic, with a 1,2-shift from boron to a heteroatom (equations 1-3) (ii) radical and (iii) electrocyclic. 

Two novel routes to triethylborane have been reported. Irradiation of bromoethane and aluminium powder with ultrasound gives ethyl aluminium sesquibromide which on treatment with triethoxyborane gives triethylborane in good yields and a laser initiated gas phase reaction between diborane and ethene gives yields of upto 91%. Allylic boranes have been prepared from allylpotassiiim derivatives and chloroboranes. Hydrolysis leads to the Isomerised olefin and the technique has been used to transform (+)-a-pinene into (+)-3-pinene. Condensation reactions between allylboranes and acetylenes have been developed into a convenient method for the synthesis of bicyclo[3.3.l]nonane derivatives. Mainly linear alkyl derivatives of 9-BBN have been synthesised from the, reaction of iron carbonyls and the organoborane in a Fischer-Tropsch type reaction. ... 

Ring expansion of 1,3,2-diazaboracycloalkanes with phenyl isocyanate and isothiocyanate has resulted via insertion of two atoms of the double bond system into the ring. Similarly, three new heterocyclic organoboranes have been produced from heterocyclic aminoboranes and organic isocyanates. The synthesis and thermal rearrangement of boron carbamoylaminopyridin-ates of the type (30) and (31) have been discussed. ... 

Organoboranes can also be used to construct carbon-carbon bonds by two other types of reactions in which a migration of an alkyl group from boron to carbon is involved. Certain -unsaturated carbonyl compounds react with trialkyl-boranes with the net transformation being transfer of one alkyl group from the borane to the / -carbon atom of the unsaturated system. A free-radical mechanism... 

---