Unidirectional thermal electrocyclic ring forming reactions of methylenecyclobutenes from vinylallenes in the retinoid series

Rey, Joaquín Pérez; Rodríguez, Jesús; Lera, Ángel R. de

doi:10.1016/s0040-4039(00)73735-x

Cited by 18 publications

(5 citation statements)

References 19 publications

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“…The reaction of 65 with R = CHO is slower. Ab initio molecular orbital studies at the 6-31G* level with the Gaussian 92 program indicated that the regioselectivity was determined by the conformations of 65 and 67 (Scheme ) 17 …”

Section: Cycloaddition Reactionsmentioning

confidence: 99%

Some Typical Advances in the Synthetic Applications of Allenes

2005

Chem. Rev.

1,353

256

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In 1989, Kakiuchi et al. reported that under irridation propadiene can undergo [2+2]-cycloaddition with R,β-unsaturated cyclohexenones to afford methylene-cyclobutane-containing bicyclic products 1 (Scheme 1). 6 Shi et al. reported that under the catalysis of DABCO, N-tosylated imines 2 can undergo [2+2]cycloaddition with 2,3-butadienoate or 3,4-pentadien-2-one to afford azetidine derivatives 3. 7 The reaction proceeded via the nucleophilic addition of DABCO to the electron-deficient allene forming 4-and 5-type intermediate, which may undergo 1,2-addition with the imines to afford 6. Intramolecular conjugate Scheme 1

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Section: Cycloaddition Reactionsmentioning

confidence: 99%

Some Typical Advances in the Synthetic Applications of Allenes

2005

Chem. Rev.

1,353

256

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“…The interconversion of cyclobutene ( 1 ) with 1,3-butadiene ( 2 ) is a reaction of great synthetic and mechanistic interest, as is the corresponding reaction of the analogous pairs methylenecyclobutene ( 3 )/vinylallene ( 4 ), bis(methylene)cyclobutene ( 5 )/bisallene ( 6 ), cyclobutenone ( 7 )/vinylketene ( 8 ), methylenecyclobutenone ( 9 )/allenylketene ( 10 ), and cyclobutenedione ( 11 )/1,2-bisketene ( 12 ). , Substituted vinylketenes in particular have become major synthetic intermediates because of their facile intramolecular cyclization with attached unsaturated substituents (Smith−Hoehn reaction). 4c-h These reactions have added significance because of their relationships to the cyclization of enediynes, enyneallenes, and enyneketenes, including derivatives with “skipped” conjugation, which have DNA cleaving ability and utility as anticancer antibiotics and are also valuable synthetic intermediates …”

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confidence: 99%

Stabilized and Persistent Allenylketenes

et al. 1997

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Photolyses of 2,3-bis(trimethylsilyl)-substituted methylenecyclobutenones 22−26 give essentially quantitative conversion to the allenylketenes 28−32 which have been isolated as long-lived species at room temperature. As predicted by molecular orbital calculations, the methylenecyclobutenones 22 and 26, with carbethoxy and hydrogen substitution on the methylene group, respectively, undergo thermal equilibration with the corresponding allenylketenes 28 and 32 with equilibrium constants [22]/[28] = 1.0 and [26]/[32] = 0.029, at 100 °C. The X-ray structure of the phenyl-substituted allenylketene 29 confirms the anti-planar conformation as predicted by calculation. The bis(allenylketene) 35 has been made by an analogous procedure. Hydration rates of the allenylketenes show acceleration by the CO2Et substituent, but in all cases these are modestly less reactive than the 1,2-bisketene (Me3SiCCO)2.

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“…These two weaknesses associated with this transformation so far detract from its practical value in the synthesis of cyclobutenes. To make this reaction a more routine synthetic method, efforts should be directed to find a unidirectional process under mild reaction conditions . Herein we disclose that the isomerization of various titanated vinylallenes (R 1 = Ti(OR) 3 in eq 1), which most likely involves the electrocyclization as above, took place smoothly even at 0 °C to give the corresponding cyclobutenyltitanium species.…”

mentioning

confidence: 85%

“…Electrocyclization of vinylallenes to methylenecyclobutenes as shown in eq 1 is a straightforward method to prepare cyclobutene derivatives from open-chain precursors. − However, this process often requires a very high reaction temperature of up to 350−450 °C, which is not recommended for routine laboratory equipment. Moreover, equilibrium between vinylallene and methylenecyclobutene tends to result in the formation of a mixture of the starting material and the product, − or the preferred production of vinylallene 1a. These two weaknesses associated with this transformation so far detract from its practical value in the synthesis of cyclobutenes.…”

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confidence: 99%