Stereochemical consequences in the pyrolysis of lactone tosylhydrazone salts

Foster, A. M.; Agosta, William C.

doi:10.1021/ja00783a061

Cited by 10 publications

(7 citation statements)

References 5 publications

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“…12-15 3,3-Dimethyl-3-sila-2-oxacyclohexylidene has been reported to undergo ring contraction, decarbonylation, and 1,2-H migration, 15 but to our knowledge, the mechanisms of these intramolecular rearrangements have never been investigated, presumably because of the assumption that they are no different from the analogous rearrangements of cyclic alkoxycarbenes. [1][2][3] The mechanism for 1,2-H migration in 3-sila-2-oxacyclohexylidene A is expected to involve a typical hydride-like shift to the "vacant" carbene p orbital. [16][17][18][19][20][21] However, the mechanisms for ring contraction and decarbonylation are expected to be a bit more complicated.…”

Section: Introductionmentioning

confidence: 99%

“…Cyclic alkoxycarbenes have been known to undergo a number of intramolecular rearrangements, including 1,2-H migration, ring contraction, and decarbonylation. − Particular attention has been paid to the mechanism of ring contraction not only because it is an intriguing problem but also because it is closely related to the photochemical ring expansion of cycloalkanones. − Experimental evidence seems to indicate that this reaction occurs via both a concerted mechanism involving an anion-like shift from oxygen to the “vacant” carbene p orbital and a stepwise fragmentation-recombination mechanism involving an acyl−alkyl biradical intermediate. − Decarbonylation is also believed to involve initial fragmentation to an acyl−alkyl biradical, which thereafter loses carbon monoxide to afford a dialkyl biradical. − The latter biradical then collapses to the appropriate cycloalkane product.…”

Section: Introductionmentioning

confidence: 99%

“…[4][5][6][7] Experimental evidence seems to indicate that this reaction occurs via both a concerted mechanism involving an anion-like shift from oxygen to the "vacant" carbene p orbital and a stepwise fragmentation-recombination mechanism involving an acylalkyl biradical intermediate. [1][2][3] Decarbonylation is also believed to involve initial fragmentation to an acyl-alkyl biradical, which thereafter loses carbon monoxide to afford a dialkyl biradical. [1][2][3] The latter biradical then collapses to the appropriate cycloalkane product.…”

Section: Introductionmentioning

confidence: 99%

“…[1][2][3] Decarbonylation is also believed to involve initial fragmentation to an acyl-alkyl biradical, which thereafter loses carbon monoxide to afford a dialkyl biradical. [1][2][3] The latter biradical then collapses to the appropriate cycloalkane product.…”

Section: Introductionmentioning

confidence: 99%

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Mechanisms of Intramolecular Rearrangements of Cyclic Siloxycarbenes

Loncke

Peslherbe

2004

J. Phys. Chem. A

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Intramolecular rearrangements of 3-sila-2-oxacyclohexylidene have been investigated using hybrid density functional theory calculations, the quantum theory of atoms in molecules, and the electron localization function. Mechanisms for 1,2-H migration, ring contraction, and decarbonylation have been examined. The mechanism for 1,2-H migration was shown to involve a typical hydride-like shift from the migration origin to the “vacant” carbene p orbital, while ring contraction was found to occur via a concerted pathway involving a front-side nucleophilic attack by the carbene lone pair at silicon as opposed to a stepwise pathway involving an acyl−silyl biradical intermediate. Decarbonylation, on the other hand, was shown to be a stepwise reaction that preferentially occurs via the intermediacy of silacyclopentanone rather than acyl−silyl and alkyl−silyl biradicals. Computed energetics and thermodynamics indicate that 1,2-H migration and ring contraction are considerably more favorable than decarbonylation. Finally, AIM analysis reveals that the changes in molecular structure associated with 1,2-H migration involving a hydride-like shift to the “vacant” carbene p orbital occur via a conflict mechanism, whereas those associated with ring contraction (or 1,2-silyl migration) involving front-side nucleophilic attack by the carbene lone pair at silicon occur via a bifurcation mechanism. The latter findings further suggest that AIM analysis may be a viable approach to unambiguously distinguish between reaction mechanisms.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Mechanisms of Intramolecular Rearrangements of Cyclic Siloxycarbenes

Loncke

Peslherbe

2004

J. Phys. Chem. A

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“…Homolysis of cyclic oxycarbenes, generated by the photolysis of cycloalkanones, to acyl alkyl biradicals has been suggested 4,5 and established. 6 Ring opening of cyclic oxy- [7][8][9][10] and dioxycarbenes 11 has been proposed in a number of cases where the carbenes were generated by the pyrolysis of tosylhydrazones at temperatures ranging from 190 to 210 °C. It has also been proposed that acyclic oxy-and dioxycarbenes decompose to radical pairs when generated thermally by the tosylhydrazone route at 158 and 175 °C in solution.…”

Section: Introductionmentioning

confidence: 99%

A Theoretical Study of Hydroxycarbene as a Model for the Homolysis of Oxy- and Dioxycarbenes

2000

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Recent work has shown that dioxycarbenes can readily undergo homolytic fragmentations to radicals in solution. Previous workers have found some theoretical evidence for a transition state in the homolysis of dihydroxycarbene to HOCO and H radicals using the CISD method, but they were not able to conclude whether such a barrier was real or an artifact of the approximation. In this work the homolysis of hydroxycarbene is examined at the CAS and MRCI levels of theory using the cc-pVDZ basis set. The atomic and molecular properties are examined using the theory of atoms in molecules. At the highest level of theory, a transition state is found for the fragmentation of trans-but not of cis-hydroxycarbene. This transition state is rationalized in terms of the electronic states involved in the avoided crossing and by examining the evolution of several atomic and molecular properties during the homolysis. It is concluded that its origin can be traced to a mismatch of the electronic structures of these states in the region of the avoided crossing, best expressed by the dipole moments.

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