Reactions of dimethoxycarbene and fluoromethoxycarbene with hydroxyl compounds. Absolute rate constants and the heat of formation of dimethoxycarbene

Du, Xue Mei; Fan, Hong; Goodman, Joshua L.; Kesselmayer, M. A.; Krogh‐Jespersen, Karsten; LaVilla, Joseph A.; Moss, Robert A.; Shen, S.; Sheridan, Robert S.

doi:10.1021/ja00161a042

Cited by 84 publications

(44 citation statements)

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“…The interactions of the p electrons of the substituents with the p p orbital at the carbene carbon atom result in the formation of a four-electron-three-center p system in which the X À C bonds acquire partial multiple bond character (Scheme 2). Important members of this class of compounds are the dimethoxycarbenes [12] and the dihalocarbenes. [13] The Nheterocyclic carbenes which form the centerpiece of this review (for a theoretical treatment of N-heterocyclic carbenes with a five-membered carbene ring see reference [14]) contain for geometric and electronic reasons exclusively X 2 CD singlet carbene centers (Scheme 2).…”

Section: Introductionmentioning

confidence: 99%

Heterocyclic Carbenes: Synthesis and Coordination Chemistry

2008

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The chemistry of heterocyclic carbenes has experienced a rapid development over the last years. In addition to the imidazolin-2-ylidenes, a large number of cyclic diaminocarbenes with different ring sizes have been described. Aside from diaminocarbenes, P-heterocyclic carbenes, and derivatives with only one, or even no heteroatom within the carbene ring are known. New methods for the synthesis of complexes with N-heterocyclic carbene ligands such as the oxidative addition or the metal atom template controlled cyclization of beta-functionalized isocyanides have been developed recently. This review summarizes the new developments regarding the synthesis of N-heterocyclic carbenes and their metal complexes.

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Section: Introductionmentioning

confidence: 99%

Heterocyclic Carbenes: Synthesis and Coordination Chemistry

2008

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“…Studies of the effect of fluorine substitution on the properties of carbenes and nitrenes using direct spectroscopic methods have been described by several authors. [13,14] Here we describe the matrix isolation and spectroscopic characterization of the halogenated derivatives 4-oxo-2,3,5,6-tetrafluorocyclohexa-2,5-dienylidene 1 b and 4-oxo-2,3,5,6-tetrachlorocyclohexa-2,5-dienylidene 1 c as examples of highly electrophilic triplet carbenes. the IR at 2108 cm À1 (n NÀN ) and 1325 cm À1 (n CÀF ).…”

Section: Introductionmentioning

confidence: 99%

4-Oxo-2,3,5,6-tetrafluorocyclohexa-2,5-dienylidene—A Highly Electrophilic Triplet Carbene

et al. 2000

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The 4-oxocyclohexa-2,5-dienylidenes are an interesting class of highly electrophilic carbenes. We investigated the reactivity of the 2,3,5,6-tetrafluorinated and -tetrachlorinated derivatives 1b and 1c with small molecules under conditions of matrix isolation. The reactions with molecular oxygen and with carbon monoxide produce the expected carbonyl O-oxides and ketenes, respectively. As a result of the extreme electrophilicity of 1b and c both carbenes insert with no or very small activation barriers into H2 or the CH bonds of hydrocarbons. Obviously, spin restrictions for these formally spin-forbidden reactions do not result in substantial thermal activation barriers.

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“…Nevertheless, the absolute value of that rate constant could still be substantial, given that rearrangement of benzyl-'Small changes in the assumed bond angles do not affect the sense of the change of angle strain. The rate constant for trapping of singlet dimethoxycarbene with methanol has a value =lo5 M-' s-' at 20°C (14). Assuming that dimethoxycarbene is an adequate model for 2a and that the rate constant at 100°C would be about lo6 M-' s-I, the experiment with 3.3 M methanol suggests that the rate constant for 1,2-H migration in 2a has a value 5 1 .…”

Section: Methods Results and Discussionmentioning

confidence: 96%

Azetinone formation is not competitive with intermolecular reactions of a β-lactam-4-ylidene

Zoghbi¹,

Warkentin²

1992

Can. J. Chem.

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.3-Phenoxy-I-phenyl-2-azetidinon-4-ylidene (P-lactam-4-ylidene) 2a, was generated by thermolysis of a spiro-fused p-lactam oxadiazoline precursor (1). Fast 1,2-H migration, a characteristic reaction of singlet carbenes that would convert 2a to 3-phenoxy-1-phenyl-3-azetin-2-one (4a) could not be demonstrated. Added 1, 3-diphenylisobenzofuran (6) did not afford the [4+2] cycloadduct (7) expected from 4a but, instead, the isomeric E-and Z-4-[1-(2-benzoylpheny1)-l-phenyl]-methylene-3-phenoxy-l-phenylazetidin-2-ones (9). Those compounds can be rationalized as the products of rearrangement of first-formed [2+ 11 adducts of 6 and the ylidene. The structure of the Z isomer of 9 was established by means of single crystal X-ray diffraction. Generation of 2a in methanol-d4, either neat or 3.3 M in benzene, afforded the isomeric products of carbene insertion into the OD bond of methanol-d4. Structural isomers expected from addition of methanol-d4 to 4a could not be detected. The results suggest that 1,2-H migration in 2a is relatively slow, with kH 5 1.4 x lo6 s-I at 100"C, which is slower than analogous rearrangement of benzylchlorocarbene by 200-fold or more.MICHEL ZOGHBI et JOHN WARKENTIN. Can. J. Chem. 70, 2792Chem. 70, (1992.La thermolyse d'une oxadiazoline spiro-condensee a une p-lactame (1) conduit au 3-phCnoxy-l-phCnyl-2-azCtidon-4-ylidbne (P-lactam-4-ylidbne) (2a). On n'a pas pu mettre en Cvidence de migration rapide 1,2-H, une reaction caracteristique des carwnes singulets qui permettrait de transformer le compost 2a en 3-phenoxy-1-phCnyl-3-azCtin-2-one (42). L'addition de 1,3-diph6nylisobenzofurane (6) n'a pas permis d'isoler le cycloadduit [4+2] (7) que l'on pourrait attendre 2 partir du produit 4a; on a plut6t obtenu les E-et Z-4-[1-(2-benzoylphCnyl)-1-phCnyl]-m&thylbne-3-phCnoxy-1-phknylazetidin-2-ones isombres (9). On peut rationaliser la formation de ces produits par une transposition des adduits [2+ I ] du produit 6 et de l'ylidkne qui se foment en premier. On a dCterminC la structure de l'isombre Z du composC 9 grdce 2 la diffraction des rayons X par un cristal unique. La gCn6ration du composC 2a dans du methanol-d4, soit a 1'Ctat pur ou en solution 3,3 M dans le benzbne, fournit des produits d'insertion du carbbne dans la liaison OD du methanol-d;. On n'a pas pu ditecter les isombres de structure que l'on pourrait attendre lors de l'addition du methanold4 sur le composC 4a. Les resultats suggbrent que la migration 1,2-H dans le compose 2a est relativement lente, alors que kH 5 1,4 X lo6 s-I, 2 100°C; cette valeur est 200 fois plus faible que celle observke lors de la transposition analogue du benzylchlorocarbbne.[Traduit par la rCdaction]Despite intense interest and activity in the area of p-lactam chemistry (for post-1980 reviews, see ref. I), P-lactam-4-ylidenes, 2 , were described only recently (2). They can be generated efficiently and conveniently by heating spiro-Plactam oxadiazolines (1) at ca. 100°C in solution, Scheme 1, and they have considerable potential for elaboration of the p-lactam syste...

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Reactions of dimethoxycarbene and fluoromethoxycarbene with hydroxyl compounds. Absolute rate constants and the heat of formation of dimethoxycarbene

Cited by 84 publications

References 1 publication

Heterocyclic Carbenes: Synthesis and Coordination Chemistry

Heterocyclic Carbenes: Synthesis and Coordination Chemistry

4-Oxo-2,3,5,6-tetrafluorocyclohexa-2,5-dienylidene—A Highly Electrophilic Triplet Carbene

Azetinone formation is not competitive with intermolecular reactions of a β-lactam-4-ylidene

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