Chemistry of (2- and 3-furyl)methylenes and (2- and 3-thienyl)methylenes

Hoffman, Robert V.; Orphanides, Gus George; Shechter, Harold

doi:10.1021/ja00493a023

Cited by 62 publications

(36 citation statements)

References 2 publications

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“…This is supported by the observation that treatment of the aldehyde 20c with trimethyl phosphite without the rigorous exclusion of moisture leads to cyclisation and formation of the bisphosphonate 25. Although the ring opening of thiophen-2-yl carbenes has been reported 12 we saw no evidence for this occurring with the thiophen-2-yl carbene intermediate 4a generated by the action of trialkyl phosphite on the aroylphosphonate 1a. We have therefore ruled out a pathway analogous to that shown in Scheme 8 to explain the formation of the corresponding thiophene-based bisphosphonate 10.…”

Section: Methodscontrasting

confidence: 66%

Electron-rich heteroaroylphosphonates and their reaction with trimethyl phosphite

et al. 2008

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Dialkyl heteroaroylphosphonates based on thiophene, pyrrole or furan have been prepared and their reactions with trimethyl phosphite investigated. Deoxygenation of the carbonyl groups in these heteroaroylphosphonates occurs to give carbene intermediates, which then undergo further reaction. In the case of the furan-3-oylphosphonates and those systems containing a thiophene or pyrrole ring, the major reaction pathway involves intermolecular trapping of the carbene intermediates by the trimethyl phosphite, leading to the formation of ylidic phosphonates that can be readily converted into the corresponding 1,1-bisphosphonates. However, in some furan-2-oylphosphonates the carbenes generated undergo ring-opening to initially give acyclic alkynylphosphonates which may react further to give other novel phosphorus compounds. The effects of substituents on the extent to which intermolecular trapping of the initially formed carbene competes with intramolecular rearrangement has been investigated. The latter process appears to be suppressed by a substituent at the 5-position of the furan ring, the resulting ylidic phosphonates being a rare example of an efficient intermolecular trapping of a furan-2-yl carbene.

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Section: Methodscontrasting

confidence: 66%

Electron-rich heteroaroylphosphonates and their reaction with trimethyl phosphite

et al. 2008

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“…21,22 The intermediacy of the corresponding thienyl- and furylcarbenes was inferred from the isolation of the products of insertion into the C–H bond of cyclooctane and the formal products of dimerization. Fragmentation of the ring, to afford ring-opened products, was also observed.…”

Section: Introductionmentioning

confidence: 99%

Photochemistry of Furyl- and Thienyldiazomethanes: Spectroscopic Characterization of Triplet 3-Thienylcarbene

et al. 2012

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Photolysis (λ > 543 nm) of 3-thienyldiazomethane (1), matrix isolated in Ar or N2 at 10 K, yields triplet 3-thienylcarbene (13) and α-thial-methylenecyclopropene (9). Carbene 13 was characterized by IR, UV/vis, and EPR spectroscopy. The conformational isomers of 3-thienylcarbene (s-E and s-Z) exhibit an unusually large difference in zero-field splitting parameters in the triplet EPR spectrum (|D/hc| = 0.508 cm−1, |E/hc| = 0.0554 cm−1; |D/hc| = 0.579 cm−1, |E/hc| = 0.0315 cm−1). Natural Bond Orbital (NBO) calculations reveal substantially differing spin densities in the 3-thienyl ring at the positions adjacent to the carbene center, which is one factor contributing to the large difference in D values. NBO calculations also reveal a stabilizing interaction between the sp orbital of the carbene carbon in the s-Z rotamer of 13 and the antibonding σ orbital between sulfur and the neighboring carbon—an interaction that is not observed in the s-E rotamer of 13. In contrast to the EPR spectra, the electronic absorption spectra of the rotamers of triplet 3-thienylcarbene (13) are indistinguishable under our experimental conditions. The carbene exhibits a weak electronic absorption in the visible spectrum (λmax = 467 nm) that is characteristic of triplet arylcarbenes. Although studies of 2-thienyldiazomethane (2), 3-furyldiazomethane (3), or 2-furyldiazomethane (4) provided further insight into the photochemical interconversions among C5H4S or C5H4O isomers, these studies did not lead to the spectroscopic detection of the corresponding triplet carbenes (2-thienylcarbene (11), 3-furylcarbene (23), or 2-furylcarbene (22), respectively).

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“…This assignment was confirmed by calculations at the B3LYP/6−31G(d) level of theory, which nicely reproduced the experimental spectrum (Table 1, Figure 1). The calculations also revealed that 2c had been formed in its ( Z ) configuration, in conformity with ( Z )‐ 2a , which is the primary photoproduct of the photolysis of 3a 13. However, while UV irradiation of ( Z )‐ 2a rapidly led to ( E )/( Z ) isomerization, ( Z )‐ 2c was remarkably stable, even towards prolonged UV irradiation.…”

Section: Resultsmentioning

confidence: 92%