Intramolecular Reaction of Silanol and Triarylborane: Boron−Aryl Bond Cleavage and Formation of a Si−O−B Heterocyle

Abstract

o-(Hydroxydimethylsilyl)(dimesitylboryl)benzene (1) underwent intramolecular cyclization to give 5,5dimesityl-2,2-dimethyl-3,4-benzo-1,2,5-oxasilaboracyclopentene (4) and mesitylene by boron-aryl bond cleavage. Whereas triethylamine as an additive accelerated the cyclization, DBU stabilized a silyloxyborate complex, 1,8-diazabicyclo[5.4.0]-7-undecenium 5,5-dimesityl-2,2-dimethyl-3,4-benzo-1,2,5-oxasilaboratacyclopentene, which was characterized by X-ray crystallographic analysis and HF calculations. The deuterium-labeling experiments revealed that the hydrogen migrated from the hydroxyl group in 1 to the leaving mesitylene.

Intramolecular Activation of C–O Bond by ano-Boryl Group ino-(Alkoxysilyl)(diarylboryl)benzenes

“…Recently, we synthesized o -(hydrosilyl)­(diarylboryl)­benzene, 1 , in which the dimesitylboryl and hydrosilyl groups were linked through an o -phenylene skeleton . The Si–H bond was activated by the boryl group for several types of reactions (Scheme ): (i) dehydrogenative condensation with alcohols to form 2 (R = Me ( a ); i -Pr ( b )), (ii) nucleophilic displacement by a fluoride ion to form 3 , and (iii) H-Mes exchange between the hydrogen atom on the Si atom and mesityl (Mes) group on the boron atom…”

Heteroelement Analogues of Benzoxaborole and Related Ring Expanded Systems

“…Benzosiloxaboroles are silicon analogues of benzoxaboroles where the carbon atom in a boracyclic ring is replaced by a silicon atom, thus resulting in the formation of a B-O-Si linkage. The first benzosiloxaborole derivative bearing mesityl group at the boron atom (49) was synthesized in 2008 (Scheme 17) [37,38]. The starting 1-dimesitylboryl-2-(dimethylsilyl) benzene (47) was subjected to hydrolysis of the Si-H bond followed by ring closure effected through an attack of silanol on one of the B-Mes bonds, yielding mesitylene as a byproduct.…”

“…Scheme 13. Synthesis and transformation of a boracyclic system (38) featuring B-O-B linkage attached to bicyclohexene-peri-naphthalene scaffold.…”

Synthesis and Applications of Group 14-metalated Arylboranes

“…In the latter reaction mesitylene is formed due to the B Mes bond cleavage effected by the the hydroxyl proton. It was found that the protonolysis was accelerated by NEt 3 where as the addition of DBU stabilized a crystalline silyloxyborate complex 132 (Scheme 56) [123].…”