6- fulvene, reaction aldehydes with

Interesting formation of the fulvene 422 takes place by the reaction of the alkenyl bromide 421 with a disubstituted alkyne[288]. The indenone 425 is prepared by the reaction of o-iodobenzaldehyde (423) with internal alkyne. The intermediate 424 is formed by oxidative addition of the C—H bond of the aldehyde and its reductive elimination affords the enone 425(289,290]. 

Phenylcyclopent[c]azcpine (33a) and 6,7-fused cyclopentazepines 33b-d are formed in moderate yields in a one-pot, two-stage process involving initial condensation of triphenyl-[(l-phenylvinyl)imino]phosphoranes 32 with 6-(dimethylamino)fulvene-2-carbaldehyde (30), followed by an intramolecular aza-Wittig reaction of the iminophosphorane with the pendant aldehyde function.5 The method fails with the unsubstituted vinylphosphorane 32 (R1 = R2 = H). 

Diazene 19 was synthesized in the manner portrayed below. Thus, treatment of anhydride 20 with sodium borohydride selectively reduces one carbonyl to a methylene unit. Reduction of the resulting lactone with DIBAL followed by a Wittig reaction and oxidation with PCC afforded aldehyde 22. When treated with cyclopentadiene in the presence of diethylamine in methanol, 22 undergoes a smooth and efficient conversion to fulvene 23. Diels-Alder cycloaddition to the azodicarboxylate 24 proceeded rapidly, a characteristic of reactions with this electron deficient chlorinated dienophile [8]. Selective reduction of the endocyclic n bond using diimide generated in situ, followed by the electrochemical reductive cleavage of the biscarbamate led to diazene 19 [6]. 

Diazene 63 was prepared in short order from readily available starting materials. Thus, acid 64, prepared in a standard manner from the isobutyric acid dianion and 3-methyl-3-butenyl p-toluenesulfonate, was first reduced with lithium aluminum hydride and then oxidized by using PCC/Celite to afford the expected aldehyde in 88% yield. In preparation for the Diels-Alder reaction that was to be used to assemble the bicyclic framework found in 63, the aldehyde was converted to fulvene 65. Initially, we attempted to accomplish this objective using methodology... 

Condensation via the Methyiene Group. Because of the resonance stabilization of the 71 electron system, the cyclopentadienyl anion forms readily from CPD after the dissociation of the acidic methylene proton. Under alkaline conditions, CPD undergoes condensation reaction with carbonyl compounds, such as ketones and aldehydes, yielding a family of highly colored fulvene derivatives (26). 

Cinnamils (162) have surprisingly been found to evolve towards 2,3,8-triaryl vinyl fulvenes (163) and o-terphenyl derivatives (164) under NHC catalysis. The formation of these products has been rationalized via a mechanism involving a complex cascade process. Finally, a mechanistic investigation has been carried out on the NHC-catalysed aerobic oxidative esterification of aromatic aldehydes.Aryloin species have not only been identified as key intermediates of such oxidative reactions, but most importantly is that they have been shown to be the species which react with oxygen in the air and not the Breslow intermediates as previously suggested. 

The cyclopentadienide anion, generated from cyclopentadiene and potassium hydroxide with catalytic 18-crown-6 in THF, a solid-liquid two-phase system, reacts with ketones to furnish fulvenes in moderate yields. Aldehydes cannot be used in place of ketones owing to competing condensation and polymerization reactions. ... 

Pentalenes.—The X-ray structure of the tri-t-butylpentalene (60) has been determined the compound is planar and the double bonds are localised. Pentalenes (62), together with dimers, are produced by the action of acetylenes RC=CH (R = C02Me, CHO, or CN) on l,3-di-t-butyl-6-dimethylamino-fulvene (61). The aldehyde (62 R = CHO) dimerized to yield mainly compound (63), whereas the head-to-tail dimer (64) was isolated from the cyano-derivative (62 R = CN). The latter adds water under acidic conditions to give the alcohol (65), while dimethylamine affords the rearranged adduct (66). Cycloaddition reactions of the pentalene di-ester (67) proceed differently with dicyanoacetylene and cyclopentadiene the former yields the cyclobutene derivative (68), the latter the Diels-Alder product (69). ... 

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