Au Nanoparticle‐Catalyzed Silaboration of Aryl‐Substituted Cyclopropyl Aldehydes Forming Rearranged β‐Boronate Silyl Enol Ethers

Abstract

2-Aryl-substituted cyclopropyl aldehydes undergo an unprecedented Au nanoparticle-catalyzed silaboration leading to rearranged linear -boronate-bearing silyl enol ethers. For- [a] 7233 Scheme 6. Lack of reactivity in the attempted Au/TiO 2 -catalyzed silaboration of cyclopropanecarboxaldehyde (11).

Activation of the Si–B interelement bond related to catalysis

“…A year after that, this research group took advantage of this radical pathway in a gold-catalysed silaboration of arylsubstituted cyclopropyl aldehydes, which involves a radicalclock-type rearrangement (188a-f -189a-f, Scheme 59). 77 This gold-catalysed procedure proceeded smoothly in the presence of Au/Ti 2 O nanoparticles, providing a library of b-boronatetethered silyl enol ethers in synthetically useful yields. This silaboration products were found to be labile during the purification, delivering the corresponding aldehydes by hydrolytic deprotection.…”

Substitution-Dependent Ring-Opening Hydrosilylation or Dehydrogenative Hydrosilylation of Cyclopropyl Aldehydes and Ketones Catalyzed by Au Nanoparticles

“…Our group has recently reported that the Au/TiO 2 -catalyzed silaboration of aryl-substituted cyclopropyl aldehydes gives acyclic β-boronate silyl enol ethers via ring-opening of the cyclopropane ring (Scheme ). A very similar ring-opening borylation concept with methoxypinacolborane has been reported more recently in the case of aryl cyclopropane carboxamides using Na metal as a one-electron donor . Given the facile activation of hydrosilanes on Au nanoparticles, which enables their addition on a variety of functional groups, in this manuscript, we report our studies regarding the reaction between cyclopropyl aldehydes or ketones with hydrosilanes using supported Au nanoparticles on titania (Au/TiO 2 ) as the catalyst.…”

“…The current example provides an additional paradigm of Au nanoparticle-catalyzed reactions in which ring-opening of the cyclopropane ring is observed. 14,21 Following the interesting hydrosilylation result of phenylsubstituted aldehyde 1a relative to parent 1b, we examined the reaction of PhMe 2 SiH with a series of aryl-substituted cyclopropyl carbonyl compounds (Table 1 connected to the aryl ring, even in the cases of substrates 1k and 1l, for which there is a methyl substituent on the adjacent cyclopropyl carbon. While an aryl substituent on parent cyclopropanecarbaldehyde (1b) appears necessary to obtain the ring-opening hydrosilylation pathway with selective cleavage of the cyclopropyl C(Ar)−C(carbonyl) bond, we also attempted to examine the influence of an alkyl group in the reaction outcome.…”

β-Borylation of conjugated carbonyl compounds with silylborane or bis(pinacolato)diboron catalyzed by Au nanoparticles

“…This is a typical characteristic of Au/TiO 2 in a series of reactions involving silylboranes or bis( pinacolato) diboron. [3][4][5][6][7] The activation of the diboron reagent pinBBpin with nano Au(0) materials has been well established in its reaction with alkynes, 18 allenes 4 and methylene cyclopropanes. 19 The β-borylation of conjugated carbonyl compounds using pinBBpin as the boron source is also known in the literature applying several catalytic protocols.…”

“…Thus, we have additionally shown (Scheme 1) the regioselective silaboration of allenes, 4 the regioselective ring opening of epoxides and oxetanes yielding βor γ-silyloxy boronates respectively, 5 the pinacol-type reductive dimerization of aryl substituted carbonyl compounds promoted by the silylborane, 6 and more recently, the silaboration of 2-aryl-substituted cyclopropyl aldehydes, in which β-boronate silyl enol ethers are formed via ring-opening rearrangement of an intermediate α-silyloxy cyclopropyl radical. 7…”