2-Oxacyclopentylidene

Oxacyclopentylidene, 234 Butane-2,3-bisacetal, 235 Cyclohexane-1,2-diacetal, 235 Dispiroketals, 236... 

In 1985, Dbtz et al. reported during a study on the reaction of Fischer-type carbene complexes with alkynes [10] that 2-oxacyclopentylidene chromium complex 24 was obtained as a side product. Thus, treatment ofmethyl(methoxy)carbene complex with 3-butynol at 70 °C in dibutyl ether gave the cyclic carbene complex 24 in 23% yield along with the desired metathesis product 23. The authors briefly commented that the cyclic carbene complex 24 might be obtained through the vinylidene complex 25, generated by the reaction of the alkyne with the liberated pentacarbonylchromium species (Scheme 5.7). 

Most efforts to explore the reactivity of ruthenium carbene complexes have employed the alkoxycarbene species so readily synthesized from the inter- or intramolecular reaction of vinylidene complexes with alcohols. These electrophilic alkoxycarbene complexes exhibit only limited reactivity at Ca, primarily with hydride reagents. For example, treatment of the 2-oxacyclopentylidene complex 97 with NaAlH2(OCH2CH2OMe)2 affords the neutral 2-tetrahydrofuranyl complex (98) [Eq. (89)] (55), as was anticipated from similar reductions of iron carbene complexes (87). 

C. P. Casey, and R. L. Anderson, Thermolysis of (2-Oxacyclopentylidene)-pentacarbo-nylchromium(O) Evidence Against Free Carbenes in Thermal Decomposition of Metal-Carbene Complexes, J. Chem Soc., Chem. Comm. 1975, 895-896. 

FIGURE 10.10 Face differentiation on methylene-2-oxacyclopentylidene chromium complexes 119 (Scheme 10.39, Ref. [91]). 

Weyershausen, B, Nieger, M, Doetz, K H, Stereospecific exo-selective Diels-Alder reactions with carbohydrate-functionalized a-exo-methylene-2-oxacyclopentylidene chromium complexes, J. Org. Chem., 64, 4206-4210, 1999. 

Methoxymethylene, 346 Ethoxymethylene, 346 2-Oxacyclopentylidene, 347 Dimethoxymethylene, 348 1-Methoxyethylidene, 348 1-Ethoxyethylidine, 348 Methylidene, 348 Phthalide, 349... 

Carbene anions react with ethylene oxide to give 2-oxacyclopentylidene complexes (Anderson and Casey, 1974b). The reaction can be envisioned as nucleophilic attack of the carbene anion on the epoxide, followed by intramolecular displacement of methoxide from the intermediate adduct. As expected for a nucleophilic attack, propylene oxide is attacked by carbene anions at the least hindered carbon atom. 

To test for the intermediacy of free carbenes in the decomposition of metal-carbene complexes, the thermolysis of the 2-oxacyclopentylidene complex XVII was studied (Anderson and Casey, 1975). 2-Oxacyclopentylidene has been generated by pyrolysis of the sodium salt of butyrolactone tosylhy-drazone and shown to rearrange to give both dihydrofuran and cyclobutanone (Agosta and Foster, 1972). The thermolysis of XVII in decalin at 180° for 15... 

C21H3iFgOPPt, trans-(Methyl(2-oxacyclopentylidene)bis(dimethylphen-ylphosphine)platinum(II)) hexafluorophosphate, 40B, 712 C21H3uFsNPaPt, trans-(Methyl(methyl-N,N-dimethylaminocarbene)bis(di-methylphenylphosphine)platinum(II)) hexafluorophosphate, 40B, 713 C2iHa9PPd, ( -Cyclopentadienyl)(7 -2-t-butylallyl)triisopropylphos-phinopalladiumdl), 46B, 1263... 

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