Acylation of alkynes by cationoid reagents with the formation of cyclopent-2-enone derivatives

SCHEGOLEV, A. A.; Smit, W. A.; Roitburd, G. V.; Kucherov, V. F.

doi:10.1016/s0040-4039(01)91910-0

Cited by 40 publications

(15 citation statements)

References 3 publications

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“…Intermediate 26 is attacked by propyne to yield the vinylic carbocation 27 , which in turn generates 28 by means of a 1,5‐hydride shift. A 1,5‐hydride shift was previously proposed in a similar system in a 1974 report39a by several of the coauthors. In the AgBF 4 system, 28 is attacked by a BF bond (similar to the Sandmeyer reaction) to yield the aliphatic fluoride 23 .…”

Section: Ch Functionalization By Intramolecular Hydride Transfersupporting

confidence: 55%

CH Bond Functionalization through Intramolecular Hydride Transfer

2014

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Known for over a century, reactions that involve intramolecular hydride-transfer events have experienced a recent resurgence. Undoubtedly responsible for the increased interest in this research area is the realization that hydride shifts represent an attractive avenue for C-H bond functionalization. The redox-neutral nature of these complexity-enhancing transformations makes them ideal for sustainable reaction development. This Review summarizes recent progress in this field while highlighting key historical contributions.

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Section: Ch Functionalization By Intramolecular Hydride Transfersupporting

confidence: 55%

CH Bond Functionalization through Intramolecular Hydride Transfer

2014

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“…They discussed a 1,5-hydride shift of the initially formed acyl vinyl cation followed by an additionelimination reaction A D E or alternatively an intramolecular electrophilic substitution S E i. [11] In our case both mechanistic alternatives can be excluded with certainty. Cyclopentene derivatives formed as products of a S E i reaction were not observed even in trace amounts.…”

Section: Intramolecular Concerted Insertion Of Vinyl Cations Into C àmentioning

confidence: 72%

Intramolecular Concerted Insertion of Vinyl Cations into CH Bonds: Hydroalkylating Cyclization of Alkynes with Alkyl Chloroformates To Give Cyclopentanes

2006

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CÀH insertions with formation of a new CÀC bond are of topical interest.[1] At present, great efforts are devoted to developing the transition-metal-catalyzed CÀH insertion. [2] The insertion of carbenes into CÀH bonds proceeds by direct attack of a nonactivated C sp 3 À H bond and formation of a new CÀC bond in a concerted one-step reaction. [3] Theoretical studies [4,5] as well as experimental investigations in the gas phase [6] have shown that the vinyl cation C 2 H 3 + can insert into the HÀH bond by formation of the ethyl cation [4,6] and into the CÀH bond of methane and of ethane by formation of the 2-propyl cation [6] and the 2-butyl cation, [5] respectively. Recently we reported on the hydroalkylation of alkenes with alkyl chloroformates induced by ethylaluminum sesquichloride (Et 3 Al 2 Cl 3 ).[7] The reaction of the Lewis acid, for example, with isopropyl chloroformate (1 a) gives the isopropyl cation, which adds across the alkene. Transfer of a hydride ion from an ethylaluminum sesquichloride species to the adduct carbenium ion takes place by formation of the hydroalkylation product (Scheme 1).The application of this reaction to alkynes was expected to give analogously alkylated alkenes. The reaction of 4-octyne (2 a) and 1 a under similar reaction conditions in the presence of Et 3 Al 2 Cl 3 and with Et 3 SiH as an additional hydride donor [8] was expected to proceed via vinyl cation 3 a to give 4-isopropyl-4-octene (4 a) (Scheme 2). To our surprise this product was formed only as a side product (< 5 %). We isolated 1-isopropyl-2-propylcyclopentane (5 a) in 79 % yield as a mixture of two diastereomers in a ratio of 4.6:1. The analogous reaction of 5-decyne (2 b) afforded the 1,2,3-trialkyl-substituted cyclopentane 5 b in 74 % yield as a mixture of four diastereomers in a ratio of 11:6:1:1. In this case, too, the hydroalkylation product 4 b was formed in only trace amounts (< 2 %). The analogous reaction of 3-hexyne (2 c) gave chloroalkene 6 c as a diastereomeric mixture (1.3:1) in 38 % yield. The hydroalkylation product 4 c was obtained in about 12 % yield. Reaction of 1-octyne (2 d) with 1 a in the presence of Et 3 Al 2 Cl 3 afforded the chloroalkylation product 6 d in 40 % yield as a diastereomeric mixture and about 5 % of the hydroalkylation product 4 d. A cyclopentane derivative or another cyclic product was not observed in either reaction.

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“…We hypothesized that a β-hydroxy-α-diazo ketone that lacks a fragmentation-promoting group at the γ position might instead react by a C–H insertion pathway. This hypothesis was based on Schegolev's initial reports 29 – 31 that vinyl cations, generated by the acylation of alkynes, can participate in C–H insertion reactions. 32 , 33 We began our studies by preparing diazo ketones 1 and 3 ( Scheme 1 ) by adding lithiated 1-diazo-3,3-dimethyl-2-butanone or lithiated 1-diazo-3-methyl-2-butanone to cyclohexanone.…”

Section: Resultsmentioning

confidence: 99%