Cyclopropanation with Gold(I) Carbenes by Retro-Buchner Reaction from Cycloheptatrienes

Solorio‐Alvarado, César R.; Wang, Yahui; Echavarren, Antonio M.

doi:10.1021/ja205046h

Cited by 145 publications

(88 citation statements)

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“…108 The retro-Buchner reaction of 7-substituted cycloheptatrienes 92 also generates gold( i ) carbenes (Scheme 29). 109 Cycloheptatrienes 92 react with gold( i ) through norcaradienes 93 to give gold( i ) carbenes 94 , which are trapped by alkenes leading to the corresponding cyclopropanes. A similar process was observed in the gas phase under electrospray ionization conditions.…”

Section: Evolution Of the Key Gold Intermediatesmentioning

confidence: 99%

Intriguing mechanistic labyrinths in gold(i) catalysis

2014

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Section: Evolution Of the Key Gold Intermediatesmentioning

confidence: 99%

Intriguing mechanistic labyrinths in gold(i) catalysis

2014

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“…10,11 In contrast, we recently found that 7-substituted 1,3,5-cycloheptatrienes 1 react with cationic gold(I) complexes under catalytic conditions through their norcaradiene tautomers 2 to generate gold(I) carbenes [LAu=CHR] + ( 3 ) in an overall retro-Buchner process (a form of retro-cyclopropanation) (Scheme 1). 12 Our discovery of this reaction was prompted by the observation of a gold(I)-promoted retro-cyclopropanation in the context of a synthesis of 1,3-disubstituted naphthalenes. 13 The retro-Buchner reaction proceeds readily with 7-aryl- and 7-alkenyl-1,3,5-cycloheptatrienes, whereas 7-alkynyl-1,3,5-cycloheptatrienes react differently with gold(I) or gold(III) catalysts to form indenes by a complex cycloisomerization that proceeds through gold-stabilized barbaralyl cations.…”

Section: Introductionmentioning

confidence: 99%

Gold(I) Carbenes by Retro-Buchner Reaction: Generation and Fate

et al. 2013

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The fate of the aryl gold(I) carbenes generated by retro-Buchner reaction of ortho-substituted 7-aryl-1,3,5-cycloheptatrienes is dependent on the constitution of the ortho substituent. Indenes and fluorenes are obtained by intramolecular reaction of highly electrophilic gold(I) carbenes with alkenes and arenes. According to density functional theory calculations, the gold-catalyzed retro-Buchner process occurs stepwise, although the two carbon–carbon cleavages occur on a rather flat potential energy surface.

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“…The observed reactivity closely resembles that previously reported for the transition-metal-catalyzed decomposition of phenyldiazomethane [26] and the cyclopropanation of stilbenes by gold carbenes generated by retro-Buchner reaction (decarbenation). [27] Thep ossible reaction mechanisms leading to cyclopropanes and the kinetically unusual formation of ethylene were examined on am odel system by means of DFT calculations (Figure 3). Initially,apurely dissociative mechanism analogous to the proposed formation of carbenes from carbenoids of Pd [28] and Ni [29] was considered.…”

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confidence: 99%

Gold(I) Carbenoids: On‐Demand Access to Gold(I) Carbenes in Solution

et al. 2017

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Chloromethylgold(I) complexes of phosphine, phosphite,a nd N-heterocyclic carbene ligands are easily synthesized by reaction of trimethylsilyldiazomethane with the corresponding gold chloride precursors.Activation of these gold(I) carbenoids with av ariety of chloride scavengers promotes reactivity typical of metallocarbenes in solution, namely homocoupling to ethylene,o lefin cyclopropanation, and Buchner ring expansion of benzene.Carbene complexes of transition metals are reactive intermediates [1] frequently invoked in awide variety of C À Cbondforming processes that range from industrial scale olefin metathesis [2] to natural product synthesis. [3] Despite their central role in gold catalysis, [4] few non-heteroatom-stabilized gold(I) carbene complexes have been structurally characterized.[5] Ther educed steric shielding provided by commonly used ligands and the intrinsically high electrophilicity [6] exhibited by simple gold(I) carbenes preclude their isolation in condensed phase.Such species are however of high interest as demonstrated by gas-phase studies by Chen, [7] Schwarz, [8] and others. [9] Theisolation of this type of compounds,ortheir functional equivalents,i st herefore of great importance for the fundamental understanding of the reactivity of electrophilic gold carbenes.T ransition-metal complexes of the type [M(CHXR)],formally defined as carbenoids, [10] show similar reactivity to their carbene counterparts [11] and offer an attractive alternative to otherwise non-isolable species.T o date,h owever, very little is known about gold(I) carbenoids and their reactivity.[12] Herein we report the synthesis of easily accessible gold carbenoids bearing bulky ligands as gold carbene equivalents in solution.Previous synthesis of chloromethylgold(I) complexes used either toxic and potentially explosive diazomethane [12a] or low-temperature in situ formation of Mg(CH 2 Cl)Cl.[12d] We have developed amore convenient approach that utilizes the methanol promoted decomposition of trimethylsilyldiazomethane [13,14] at room temperature (Scheme 1). Tr eatment of phosphine,phosphite,and NHC gold chloride complexes with trimethylsilyldiazomethane in benzene solution in presence of methanol afforded gold carbenoids 1a-d within minutes. Complexes 1a-c could be easily purified by column chromatography and have been fully characterized. Remarkably, these gold(I) carbenoids can be stored indefinitely when protected from air,a nd only decompose slowly when left under ambient conditions. Measured AuÀCd istances (Table 1) are close to 2.088-(9) observed for the previously reported [(PPh 3 )AuCH 2 Cl] complex (2).[12d] On the other hand, CÀCl distances (1.828-1.830 )are markedly longer than found in 2 (1.68(1) ), and Scheme 1. Synthesis of chloromethylgold(I) complexes 1a-d and structures of complexesa )1a,b)1b,c)and 1c.[38] ORTEP plots with ellipsoids set at 50 %p robability;h ydrogen atoms and solvent molecules are omitted for clarity.

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Cyclopropanation with Gold(I) Carbenes by Retro-Buchner Reaction from Cycloheptatrienes

Abstract: Cationic gold(I) promotes the retro-Buchner reaction of 7-substituted 1,3,5-cycloheptatrienes, leading to gold(I) carbenes that cyclopropanate alkenes.

Cited by 145 publications

References 53 publications

Intriguing mechanistic labyrinths in gold(i) catalysis

Intriguing mechanistic labyrinths in gold(i) catalysis

Gold(I) Carbenes by Retro-Buchner Reaction: Generation and Fate

Gold(I) Carbenoids: On‐Demand Access to Gold(I) Carbenes in Solution

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