Cyclopentane thermolysis

Phcnylcyclopentylamine, by hydrolysis of phenylcyclo-pentyl isocyanate, 51, 49 Phenylcyclopentyl isocyanate, by thermolysis of phenyl-cyclopentane-carboxylic acid azide, 51, 49... 

Dolbier and co-workers have studied the thermolysis of the fluorinated hexa-1,3,5-triene system using l,2-bis(trifluorovinyl)naphthalene and 9,10-bis(trifluorovinyl)phenanthrene as models. These compounds form a mixture of products thermally, of which cyclopentane derivatives... 

Thermolysis of the 3,4-dihydro-2//-thiopyran (82) in the presence of dienophiles such as maleic anhydride, styrene, and norbornene gave adducts such as (84) and (85). The thiochalcone (83) is assumed to be an intermediate. The ylide (87), prepared from methyl 6-vinylthian-2-carboxylate (86) and methyl fluorosulphonate, undergoes a 2,3-sigmatropic ring-expansion to methyl l-(methylthio)cyclohept-3-enecarboxylate (88) the cyclopentane (89) is formed as a by-product. ... 

Cyclopentane annelation. This cuprate reacts with j3-halo-a, -unsaturated ketones to form J-cyclopropylenoncs. The products rearrange on thermolysis to cyclopcnlanc systems. An example of this annelation method is formulated in equation (I). 

Interest in the cyclopentane 1,3-biradical stems not only from its ease of formation from bicyclo[2.1.0]pentane, but also its formation from 2,3-diazabicyclo[2.2.1]hept-2-ene by either thermolysis or photolysis. Remarkably, the gas phase thermolysis of xo-deuterated material gave mostly inverted bicyclo[2.1.0]pentane (Scheme 6.24). ... 

General Methods.—Trost and his co-workers have extended their earlier studies of the synthesis of cyclopentanes based on thermolysis of vinylcyclopropanes, and shown that it is expedient to use the recently developed 1-lithiocyclopropyl phenyl sulphide (32) for the preparation of the appropriate vinylcyclopropane precursor. Thus addition of (32) to ketone (33), followed by dehydration of the intermediate hydroxy-sulphide with SOCI2, led to (34), which on thermolysis in the vapour phase at 350 °C, then hydrolysis, gave the cyclopentenone (35). An identical approach to cyclopentane annelation has been used by Miller in a synthesis of (36) from cyclopent-2-enone. 

The route to cyclopentanes via thermolysis of vinylcyclopropanes is an attractive one, limited only by the availability of the vinylcyclopropane. Trost s use of (32) offers one solution to this problem, but in related investigations Piers et and also Marino and Browne, have demonstrated that the vinylcyclopropanes are smoothly produced by reaction between lithium cyclopropylcuprates (37) and jS-halogeno-ajS-unsaturated ketones, according to Scheme 13. Furthermore, Marino and Browne have found that conjugate addition of (37) to acetylenic ketones offers additional scope for the synthesis of monocyclic vinylcyclopropanes, e.g. (38) (39). 

There have been reports of a number of reactions of CPNA 73 that result in cleavage of the strained C—C o-bond under thermal conditions. The formed reactive intermediate 74 undergoes insertion and cheletropic [1+2]-, [3+2]-, and [3-1-4] cycloaddition reactions under thermal conditions (Scheme 6.13a). The reactivity profiles reported to date are consistent with such a a-delocalized singlet species 74 that can react either as a 1,1- or as a 1,3-dipole. Moreover, the 2-alkylidenecyclopropanone acetal 75 derived from a CPNA 76 is a useful precursor of dialkoxy trimethylenemethane (TMM) 77. MUd thermolysis of 75 in the presence of an electrophile generates 77, which undergoes a [3+2] cycloaddition to form cyclopentane derivative 78 (Scheme 6.13b). These results were reviewed by Nakamura and coworkers [32]. 

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