Addition reactions of ketenes

Seikaly, Hani R.; Tidwell, Thomas T.

doi:10.1016/s0040-4020(01)90545-9

Cited by 143 publications

(46 citation statements)

References 154 publications

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“…However, steric effects are large when nucleophilic attack by water in the ketene plane is impeded, and this provides strong support for the mechanism of eq. [3], as we have proposed previously (6,10).…”

Section: Discussionmentioning

confidence: 69%

“…The second phenyl is expected to stabilize both the ground state and an enolate-like transition state, but the most important effect is a large steric barrier in the plane of the ketene that cannot be avoided when two bulky phenyl groups are present. Such steric barriers are well documented both in preparative (10) and kinetic (5, 6) studies. While there might be a small steric barrier to a cyclic transition state such as 4, there is little evidence for such effects for attack perpendicular to alkenes (16) and these effects would also be cumulative, whereas for attack in the plane there is an abrupt change to a high steric barrier when two bulky groups are present, as is observed.…”

Section: Discussionmentioning

confidence: 87%

“…Previously, only by using in situ generation of ketenes these processes, and these have been recently reviewed (10). by flash photolysis of diazoketones to give arylketenes (1) or of…”

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confidence: 99%

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Hydration reactivity of ketenes generated by flash photolysis

Allen¹,

Kresge²,

Schepp³

et al. 1987

Can. J. Chem.

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. Can. J. Chem. 65, 1719 (1987). The ketenes n-BuCH=C=O, PhCH=C=O, and Ph2C=C=0 have been generated by flash photolysis and their reactivities toward water, including acid and base catalysis, have been measured in wholly aqueous media by ultraviolet spectrophotometry. The phenyl group electronically enhances the reactivity of ketenes relative to n-butyl toward water and hydroxide, but retards reaction with protic acids. The presence of bulky groups, including phenyls, on each side in the ketene plane sterically retards nucleophilic attack. The reactions are interpreted as involving in-plane attack by nucleophilic water or hydroxide in the neutral and base-induced reactions, and electrophilic protonation perpendicular to the ketene plane for the acid-catalyzed reaction. ANNETTE D. ALLEN, A. JERRY KRESGE, NORMAN P. SCHEPP et THOMAS T. TIDWELL. Can. J. Chem. 65, 17 19 (1987). Faisant appel 2 la photolyse Cclair, on a prCparC les ctttnes n-BuCH=C=O, PhCH=C=O et Ph2C=C=O; utilisant la spectrophotomCtrie ultraviolette et opCrant dans des milieux aqueux, on a mesure leurs rCactivitCs vis-2-vis de l'eau, tant sous I'influence de catalyseurs acides que basiques. Par comparaison avec le groupement n-butyle, le groupement phCnyle augmente la rtactivitC des cCt&nes vis-a-vis de l'eau et de I'ion hydroxyde; toutefois, il retarde la reaction avec les acides protiques. La prtsence de groupements encombrants, y compris les groupements phCnyles, de chaque cBtC du plan du ctttne retarde l'attaque nuclCophile. Pour expliquer les rkactions qui se produisent en milieux neutre ou basique, on fait appel i un mecanisme impliquant une attaque, par l'eau du l'hydroxyde nuclCophiles, qui se produirait dans le plan; par ailleurs, les rkactions catalysCes par les acides se produiraient par le biais d'une protonation Clectrophile qui se ferait d'une faqon perpendiculaire au plan du cCttne.[Traduit par la revue]The kinetic study of the hydration of ketenes in wholly At least partly because of the diversity of methods and conaqueous media is complicated not only by the strong tendency ditions that have been used for these studies of ketene hydration of the ketenes to dimerize but also by their high reactivity with there are also widely divergent views of the mechanisms of water. Previously, only by using in situ generation of ketenes these processes, and these have been recently reviewed (10). by flash photolysis of diazoketones to give arylketenes (1) or of We have advocated (5, 6) the processes shown in eqs.[3]-[5] cyclobutanone to give ketene (2), together with fast measure-A+ ment techniques, have such studies been accomplished (eqs.

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Section: Discussionmentioning

confidence: 69%

Section: Discussionmentioning

confidence: 87%

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Hydration reactivity of ketenes generated by flash photolysis

Allen¹,

Kresge²,

Schepp³

et al. 1987

Can. J. Chem.

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“…Steric effects of ketene substituents for nucleophilic additions at the ketene LUMO in the plane of substituents are well documented, and are proposed to be responsible for high levels of E/Z selectivities obtained in the reactions of unsymmetrically substituted ketenes with carbon and oxygen nucleophiles. 34,35 The inclusion of N-protected chiral auxiliaries leads to an increase in the E/Z selectivity by introducing a higher degree of steric hindrance at the transition structures with the Ph group cis (Fig 6, X = NBoc and NTIPBS). While the additional contribution of N-PG to the selectivity is found to be minimal for N-Boc nitrone, the steric effects become significant with the increasing size of the protecting group, disfavoring TSE-NTIPBS compared with TSZ-NTIPBS with an energetic cost that amounts to 4.0 kcal/mol.…”

Section: Computational Studies -Role Of the N-substituent In Determinmentioning

confidence: 99%

An asymmetric pericyclic cascade approach to 3-alkyl-3-aryloxindoles: generality, applications and mechanistic investigations

et al. 2015

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The reaction of L-serine derived N-arylnitrones with alkylarylketenes generates asymmetric 3-alkyl-3-aryloxindoles in good to excellent yields (up to 93%) and excellent enantioselectivity (up to 98% ee) via a pericyclic cascade process. The optimization, scope and applications of this transformation are reported, alongside further synthetic and computational investigations. The preparation of the enantiomer of a Roche anti-cancer agent (RO4999200) 1 (96% ee) in three steps demonstrates the potential utility of this methodology.

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“…[11][12][13][14][15] and the frequent postulation of metalbound vinylketenes as reaction intermediates (ref. [16][17][18], we decided that a study of the reactivity of our (viny1ketene)tricarbonyliron complexes would prove interesting and rewarding.…”

Section: Synthesis Of (Vinylketene) Tricarbonyliron Complexesmentioning

confidence: 99%

Transition metal-stabilised vinylketenes

Hill¹,

Richards²,

Thomas³

1990

Pure and Applied Chemistry

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-(Vinylketene)tricarbonyliron complexes are synthesised from readily-available (vinylketone)tricarbonyliron complexes. They react with isonitriles to give (vinylketenimine)tricarbonyliron complexes and with nucleophiles at C-1 to give p,yunsaturated carbonyl derivatives. In contrast (vinylketenimine)tricarbnyliron complexes react with nucleophiles at C-2 to give P,y-unsaturated carbonyl derivatives containing an a quaternary centre. This approach has been used to generate homochiral quaternary centres.

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Addition reactions of ketenes

Cited by 143 publications

References 154 publications

Hydration reactivity of ketenes generated by flash photolysis

Hydration reactivity of ketenes generated by flash photolysis

An asymmetric pericyclic cascade approach to 3-alkyl-3-aryloxindoles: generality, applications and mechanistic investigations

Transition metal-stabilised vinylketenes

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