Ring-contracted product

Moreover, the frequent need for further elaboration of the ring expanded or ring expanded-ring contracted products required that they have functional groups suited for subsequent chemical transformations. 

The Fuvorskii reaction involves treatment of an a-bromo ketone with base to yield a ring-contracted product, for example, reaction of 2-bromocyclo-hexanone with aqueous NaOH yields cyclopentanecarboxylic acid. Propose a mechanism. 

Though the reaction is not general, certain cyclic ketones can be photolyzed to give ring-contracted products.In the example above, the cyclobutanone (55) was photolyzed to give (56), where BZ is benzoyl. This reaction was used to synthesize tetra-r rf-butyltetrahedrane (57). 

In a reaction similar to 17-37, certain sulfones, both cyclic and acyclic, extrude SO2 on heating or photolysis to give ring-contracted products." An example is the... 

The 2-trifluoromethanesuIfonates of the four diastereomeric 3,5-di-O-benzyl-pentono-1,4-lactones (such as D-ribono-1,4-lactone, 283) gave, upon treatment with potassium carbonate in methanol, the ring-contraction product, methyl oxetane-2-carboxylate (284). The stereochemistry at C-2 of the resulting oxetanes is determined by the configuration at C-3, rather than C-2, of the starting lactones (267). 

Other approaches to alkylidenecycloproparenes have been attempted without success. Aromatization of appropriate alkylidenecyclopropanes or their precursors could not be realized, and flash vacuum pyrolysis of methylene phthalide and 3-methylene-2-coumaranone afforded rearrangement products rather than alkylidenecycloproparenes via extrusion of 002. The photochemical or thermal decomposition of the sodium salt of benzocyclobutenone p-toluenesulfonyl hydrazone led to products derived from dimerization of the intermediate benzocy-clobutenylidene, or from its reaction with the solvent, but no ring-contracted products were observed. When the adduct of methylene-l,6-methano[10]annulene to dicyanoacetylene (249) was subjected to Alder-Rickert cleavage, phenylacety-lene (250) was formed, which derives reasonably from the parent 234. ... 

When a mixture of the /ra t-epoxide 71 and triphenylphosphine was heated to reflux in CDCI3, the ring-contracted product 72 was isolated in 81% yield (Scheme 16) <2004JOC2577>. Hydrogenation of substituted 3,6-dihydro-l,2-dioxins was explored under several sets of conditions <1995SC2613> whereby a high yield was obtainable by catalytic reduction over Pt02. 

In a report from Sashida and co-workers, the unexpected ring-contracted products 112 were produced from the treatment of 111 with NaOMe at room temperature <99H2407>. This tandem ring-expansion (110 111) ring-contraction provided a facile route to... 

The oxidation of AT-substituted 5//-dibenz[6,/] azepines with MCPBA is complex and depends upon the nature of the N-substituent. AT-Acyl derivatives do not form the N-oxide but suffer epoxidation of the 10,11-bond. AT-Aryl derivatives undergo hydroxylation of the phenyl ring, whereas N-alkyl congeners, with the exception of the AT-methyl compound, yield mixtures of diphenylamines and acridones. The N-oxide is obtained from the A/-methyl derivative along with ring-opened and ring-contracted products (81CPB1221). 

Partial racemization, however, occurred in the deamination of optically active 2-aminobicy-clo[2.2.1]hept-5-ene-2-carbonitrile yielding a 1 2 mixture of the ring-contraction products 2-hy-droxybicyclo[3.1.1]hept-3-ene-l-carbonitrile (21, 40% retention of optical activity) and 4-hy-droxybicyclo[3.1.1]hept-2-ene-l-carbonitrile (22, 5% retention of optical activity). The chiral bridged cation gave only 21, while from the achiral allyl cation both 21 and 22 were formed.87... 

As discussed, electron-donating groups at Cl in bicyclo[2.2.1]heptane systems promote the rearrangement to bicyclo[3.1.1]heptane derivatives. Photolysis of 1-methyl bicyclo[2.2.1]heptan-2-one tosylhydrazone in 1,2-dimethoxyethane in the presence of sodium hydroxide gave 2-methyl-bicyclo[3.1. l]heptan-2-ol (26a) in 7.5% yield in addition to bicyclo[2.2.1]heptane derivatives, while the 1-phenyl derivative gave the ring-contracted product 26b in only 2% yield.91... 

Very highly constrained bicyclic alkenes rearrange via carbene intermediates to ring-contracted products. Thus, bicyclo[3.3.0]oct-2-ene gave 6-methylenebicyclo[3.2.0]heptane (38), and bicy-clo[2.2.1]hept-2-ene gave 5-methylenebicyclo[2.1.1]hexane (39).113... 

In a reaction similar to 7-47, certain sulfones, both cyclic and acylic,461 extrude S02 on heating or photolysis to give ring-contracted products.462 An example is the preparation of naphtho(f )cyclobutene shown above.463 In a different kind of reaction, five-membered cyclic sulfones can be converted to cyclobutenes by treatment with butyllithium followed by LiAIH4,464 e.g.,... 

In contrast, 3-tert-butyI-6-chIoropyrido[2,3-6]pyrazine rapidly reacts with KNHj-NHj to yield a ring contraction product, 2-tm-butyl-l//-imidazo[4,5-6]pyridine (Scheme 4). The transformation is reminiscent of the ring contraction undergone by 2-methylthio-4,6,7-triphenyIpteridine to yield 6,8-diphenyI-2-methyIthiopurine.120 Although no ff-adduct could... 

The investigations on the pyrido[2,3-6]pyrazine ring were inspired by the related pteridine ring, of importance in natural products. Pteridines are very reactive systems with both liquid ammonia and KNH2 in liquid ammonia, but in neither medium have anionic (j-adducts ever been detected. Such adducts presumably form initially and rapidly evolve toward covalent amination and ring contraction products.119,121... 

This conformation would, however, be expected to give the ring-contracted product. 

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