2015
DOI: 10.1021/om501096x
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Assembling Contiguous Quaternary Carbon Atoms: Regio- and Stereoselective Rearrangements in Cobalt-Directed Radical Reactions of 1,4-Enynes

Abstract: Radical coupling reactions of Co 2 (CO) 6 -complexed 1,4-enynes occur in a regio-and stereoselective fashion, providing access to 3E,7E-decadiene-1,9-diynes in excellent yields (84−99%). The formation of contiguous quaternary carbon atoms follows a tandem allylic rearrangement that projects an original reaction site gamma to the metal core. Propargyl alcohols with an α-alkenyl group as a substituent are treated with HBF 4 , followed by the reduction of the highly conjugated propargyl cations with zinc. The sco… Show more

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Cited by 10 publications
(5 citation statements)
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“…This particular coupling is unique in that it forges an all-carbon quaternary center vicinal to other quaternary centers. To the best of our knowledge, this substitution pattern has not been reported in the α-arylation literature and, in general, is a difficult motif to forge under any conditions …”
Section: Resultsmentioning
confidence: 99%
“…This particular coupling is unique in that it forges an all-carbon quaternary center vicinal to other quaternary centers. To the best of our knowledge, this substitution pattern has not been reported in the α-arylation literature and, in general, is a difficult motif to forge under any conditions …”
Section: Resultsmentioning
confidence: 99%
“…Although propargyldicobalt radicals bearing alkenyl [52] and alkynyl [53] substituents at the propargylic site may in principle react at two ( α‐ or γ‐) sites, their corresponding dimerizations exhibit a predictable pattern of reactivity. Radicals derived from enyne complexes 105 undergo remote coupling at the γ ‐site exclusively ( 106 ), regardless of whether generation is from the α‐ or γ‐ alcohol or the γ ‐methyl ether (Scheme 25).…”
Section: Reductions Of Highly Stabilized Carbocationsmentioning
confidence: 99%
“…Introducing an alkenyl group α to the metal core creates a new regioselectivity dimension in cobalt-assisted radical reactions ,, wherein the radical C–C bond formation could occur either at the site of the initial cation generation ( 95 ) or, upon an allylic rearrangement, γ to the metal core ( 96 , Figure ). Three alternative methods for the generation of requisite cations were developed, employing α-alcohol 97 , γ-alcohol 98 , and γ-Me ether 99 (Figure ) . The former represents the standard protocol wherein the cobalt complex is treated with HBF 4 , and the respective cation is isolated at low temperatures as a tetrafluoroborate salt.…”
Section: Assembling Contiguous Quaternary Carbon Centers: α-Alkenyl P...mentioning
confidence: 99%
“…Three alternative methods for the generation of requisite cations were developed, employing α-alcohol 97, γ-alcohol 98, and γ-Me ether 99 (Figure 12). 30 The former represents the standard protocol 14 adversely impact the selectivity of the radical reaction and, second, that an α,β-double bond acts as an efficient conduit between a π-bonded electron reservoir and the cationic center. Overall, radical reactions of 1,3-and 1,4-enynes, reacting with the retention and projection of the reaction active sites, respectively, allow for efficient assembly of contiguous quaternary carbon atoms, a highly sought after molecular unit in organic chemistry.…”
Section: Propargyl Acetals As Substratesmentioning
confidence: 99%