Silylboronic esters

Dimethylphenylsilyl)-4,4,5,5-tetramethyl-l,3,2-dioxaborolane (1) is prepared by reaction of dimethylphenylsilyllithium with 4,4,5,5-tetramethyl-l,3,2-dioxaborolane (pinacolborane, 2equiv) or 2-isopropoxy-4,4,5,5-tetramethyl-l,3,2-dioxaborolane (2 equiv) (eq 1). Silylboronic esters 2 and 3a are also synthesized via similar routes using methyldiphenylsilyllithium and [(diethyl-ainino)diphenylsilyl]lithium, respectively (eq 2). Diethylamino-substituted silylborane 3a is converted to a chlorine-substituted 4a by reaction with dry hydrogen chloride (eq 3). Silylborane 1 is... 

Silylboronic ester 1 reacts with allenes in the presence of a palladium catalyst bearing isocyanide or phosphorus ligands such as4-ethyl-2,6,7-trioxa-l-phosphabicyclo[2.2.2]octane (etpo) and... 

Silylboronic ester 1 adds to 1,3-dienes in the presence of platinum and nickel catalysts to give 1,4-silaboration products. A nickel(O) catalyst generated in situ from reaction of Ni(acac)2 with DIBAL is effective for the silaboration of butadiene, isoprene, and 2,3-dimethylbutadiene to give (Z)-l-boryl-4-silyl-2-butenes in high 3uelds with complete Z selectivity (eq 15). Silaboration of cyclic 1,3-dienes such as... 

Silyl Anion Equivalent. Silylboronic ester 1 reacts as a silyl anion equivalent in the presence of transition metal catalysts. Cyclic and acyclic a,/3-unsaturated carbonyl compounds serve as good acceptors of the silyl groups in conjugate addition of 1 catalyzed by rhodium and copper complexes, giving /3-silylcarbonyl compounds (eq 30). The silylation takes place with high enan-tioselectivity when Rh/(5)-BINAP or Cu/chiral NHC catalysts are used. Three-component coupling of 1, a,/3-unsaturated carbonyl compounds, and aldehydes affords 8-hydroxyketone stereoselec-tively in the presence of a copper catalyst (eq 31). The copper enolate 32 is presumed as an intermediate of the reaction. 

The silylboronic ester 1 reacts with propargylic carbonate 33 in the presence of a rhodium catalyst to give allenylsilane 34 via Sn2 reaction (eq 32). A high level of chirality transfer is attained when the enantioenriched substrate is used. Allylic chlorides also undergo Sn2 reaction with 1 using a copper catalyst, giving branched allylic silane (eq 33). ... 

Reaction with Carbenoids and Isocyanides. Silylboronic ester 1 undergoes nucleophilic attack of carbenes and carbenoids, which is followed by subsequent 1,2-migration of the silyl group to give a-silylated organoboron compounds.Reaction... 

Recently silylboronates functionalized on silicon were reported by Suginome and coworkers via the reaction of silyl lithium 379 with borate ester 380 to yield the borosilamide 381. Further transformations on the amine with HC1 furnish the chlorosilane 382, and reaction of SbFs with 382 provide the florosilane 383. The chlorosilanes 382 also react with alcohols or amines to provide the alkoxy or amine substituted silylboronates 384 and 385 respectively (Scheme 61) <20070M1291>. 

Both y-mono and disubstituted allylphosphates react with silylboronates in the presence of a copperW-heterocyclic carbene catalyst and NaOH giving y-substituted allyl-silanes with high regioselectivities (5 275 2 ratios between 80/20 and >99/1) and high enantioselectivities (86 to 95%) ee Primary and secondary alkyl, aryl, halide, acetal, and ester groups are tolerated on C,. 

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