Regioselective Diboration and Silaboration of Allenes Catalyzed by Au Nanoparticles

Abstract

Under catalysis by commercially available supported Au nanoparticles on TiO2 (1 mol %), terminal allenes undergo diboration and silaboration exclusively on the terminal double bond, in high yields and stereoselectivity. In silaboration, the boron moiety (Bpin) is attached on the terminal carbon and the silyl group on the sp-C, a regioselectivity pattern that is unusual. No ligands or additives are required, while the catalyst is recyclable and reusable. The selectivity is rationalized in terms of a π-allyl type or an η-1 complex intermediate with an apparent allylic carbocationic character, as revealed through the use of cyclopropyl allenes as sensitive probes.

Gold‐Catalyzed Cross‐Coupling Reactions: An Overview of Design Strategies, Mechanistic Studies, and Applications

“…Oxidative addition of heteroatom-heteroatom bonds to heterogeneous Au catalysts for coupling reactions Gold nanoparticles can undergo oxidative addition with BÀB, SiÀSi, SiÀB, SnÀSn, CÀSn, and other bonds more readily than with stronger CÀC, CÀH, and C-halide bonds. [399][400][401][402] Jin'sgroup also utilized their methodologies based on nanoporous Au catalysis for the efficient diboration of alkynes [403] and methylenecyclopropanes. [395] They reasonedb ased on previous reports that have shown the ability of Au I for activating the SiÀSi bond, [243,245] and the hydrolysis and alcoholysis of disilanes.…”

Supported Au Nanoparticles‐Catalyzed Regioselective Dehydrogenative Disilylation of Allenes by Dihydrosilane

“…For monosubstituted allenes, which react faster, the product selectivity dehydrogenative disilylation versus hydrosilylation varies between 65–79 %, while for 1,1‐disubstituted the same relative selectivity is higher (>80 %). The regioselectivity pattern of the current disilylation protocol on the terminal double bond of allenes is analogous to the corresponding Au/TiO 2 ‐catalyzed direct diboration or silaboration . As proved by nOe experiments, the disilylation in the case of monosubstituted allenes is highly E ‐stereoselective, and the diastereoselectivity varies from 87 to >97 %.…”

“…The regioselectivity pattern of the current disilylation protocolo nt he terminal double bond of allenes is analogoust ot he corresponding Au/ TiO 2 -catalyzed direct diboration or silaboration. [10] As provedb y nOe experiments, the disilylation in the case of monosubstituted allenes is highly E-stereoselective, and the diastereoselectiv-ity varies from 87 to > 97 %. The reactiond oes not occur in the absence of the catalyst or in the presence of the support only (TiO 2 ), therefore, the catalytic involvement of Au nanoparticles is beyond doubt.…”

Synthesis of γ‐Boryl‐Substituted Homoallylic Alcohols with anti Stereochemistry Based on a Double‐Bond Transposition

“…[2] The E/ Z geometry of allylboron species dictates the anti/syn stereochemistry of the resulting homoallylic alcohols.V arious types of allylboron reagents have been prepared and applied to allylations. [3] In particular,w hen an allylboron reagent is functionalized with another metalloid element, for example, boron, silicon, [4] or tin, [5][6][7] the metalloid element remaining in the product allows av ariety of additional synthetic manipulations.T he groups of Cheng [8] and Stratakis [9] reported that (Z)-2-boryl-substituted allylboronates were stereoselectively prepared by either the Pd-or Au-catalyzed 1,2-diboration of terminal allenes with B 2 pin 2 (Figure 1). With regard to relevant allylmetal species,H oveyda and co-workers have developed an elegant catalytic method for generating in situ (Z)-2-boryl-substituted allylcopper complexes from terminal allenes,a nd furthermore synthesized syn isomers of g-borylsubstituted homoallylic alcohols in an enantioselective manner ( Figure 1).…”

“…Thecorresponding anti-homoallylic acetate 7bb was obtained from pent-1-yne in 83 %yield. When hept-6-ynal (9) was subjected to this one-pot procedure,t he allylation step occurred intramolecularly to form the desired cyclic product, trans-2-(1-borylvinyl)cyclopentyl acetate (11). [22] Thea lkenylboron group remaining in the homoallylic alcohols could be used for subsequent synthetic derivatizations (Schemes 3a nd 4).…”