1993
DOI: 10.1021/ar00027a002
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New perspectives on carbene rearrangements: migratory aptitudes, bystander assistance, and geminal efficiency

Abstract: Singlet carbenes are commonly generated by thermolysis or direct photolysis of nitrogen-containing precursors such as diazo compounds, diazirines, and iV-aziridinylimines.1 (Because of innate instability, diazo species are often prepared and decomposed in situ.) Although carbenes can exist in three singlet electronic configurations ( 2, , p2), the 2 arrangement is favored energetically and in most cases is responsible for the chemistry of singlet carbenes, especially in condensed phases that allow rapid collis… Show more

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Cited by 111 publications
(69 citation statements)
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“…However, the ranking for the Wolff rearrangement is similar to that for 1,2-shifts of substituted alkylcarbenes, R 1 R 2 R 3 CϪCH: Ǟ R 2 R 3 CϭCHR 1 ϩ ..., in which ''bystander assistance'' of nonmigrating groups is a complicating factor. [78] Even the ''upgrading'' of alkyl groups in photochemical, relative to thermal, reactions recurs in alkylcarbene rearrangements. [79] The ranking of migratory aptitudes is still not fully understood.…”
Section: Migratory Aptitudesmentioning
confidence: 99%
“…However, the ranking for the Wolff rearrangement is similar to that for 1,2-shifts of substituted alkylcarbenes, R 1 R 2 R 3 CϪCH: Ǟ R 2 R 3 CϭCHR 1 ϩ ..., in which ''bystander assistance'' of nonmigrating groups is a complicating factor. [78] Even the ''upgrading'' of alkyl groups in photochemical, relative to thermal, reactions recurs in alkylcarbene rearrangements. [79] The ranking of migratory aptitudes is still not fully understood.…”
Section: Migratory Aptitudesmentioning
confidence: 99%
“…The compound is 4.0 kcal mol À1 more stable than 'Möbius benzene' 5 (see Pathway I). According to previous experimental and theoretical investigations, intramolecular rearrangements in carbenes proceed via the singlest state 11,12,[37][38][39] and therefore the further mechanistic considerations are restricted to the singlest state of 8.…”
Section: Intermolecular [4 2] Cycloaddition Reaction Of Conjugated Enmentioning
confidence: 99%
“…Nickon concluded, on the basis of these data and competition experiments using isotopically labeled benzylcarbene, that the intrinsic migratory aptitude of a phenyl group is actually larger than that of a hydrogen atom. 19 A significant complication in Nickon's analysis is that dialkyl and benzyl carbenes have triplet ground states. 20 This is particularly significant where competitive product yields were used to infer the relative migratory aptitudes of H and Ph groups.…”
Section: Introductionmentioning
confidence: 99%