Cyclohexene rearrangement

Cycloaddition of OTr/n-bomyltriazolinedione 706 to 9-thia-l-azabicyclo[4.2.1]nona-2,4-diene 9,9-dioxide 705 gave compound 707 as a diastereoisomeric mixture (Scheme 112). The formation is attributed to the sequential operation of a regioselective [2+2] cycloaddition and a heteroatomic variant of the vinylcyclobutane-cyclohexene rearrangement <2006JOC6573>. 

Photochemical [2 + 2] cycloadditions followed by vinylcyclobutane to cyclohexene rearrangements often yield the same products as the thermal Diels-Alder reactions. Strongly directing substituents on unsymmetrical dienes, however, may lead to constitutionally different isomers depending on the reaction path.19 21... 

Acceleration of the vinylcyclobutane to cyclohexene rearrangement of vinylcyclobutanols by conversion to the potassium alkoxide was first reported by Wilson and Mao.50 Typically, the [1,3] shift occurs at a satisfactory rate in tetrahydrofuran between room and reflux temperature. Sodium51 or lithium alkoxides52 also rearrange in this temperature range. The reaction rate can be further increased by addition of crown ethers or hexamethylphosphoric triamide.50,53... 

While carbethoxyaziridines are usually quite stable (they withstand the injection temperature of gas chromatography) other aziri-dines react further and are therefore not detected in the final products. For example, the aziridine presumably formed from pivaloyl nitrene and cyclohexene rearranges to a Schiff s base and to an amine... 

A highly successful route to stereoisomers of substituted 3-cyclohexene-l-carboxylates runs via Ireland-Claisen rearrangements of silyl enolates of oj-vinyl lactones. The rearrangement proceeds stereospeaifically through the only possible boat-like transition state, in which the connecting carbon atoms come close enough (S. Danishefsky, 1980 see also section 4.8.3, M. Nakatsuka, 1990). 

The reaction of cyclohexene with the diazopyruvate 25 gives unexpectedly ethyl 3-cyclohexenyl malonate (26), involving Wolff rearrangement. No cyclo-propanation takes place[28]. 1,3-Dipolar cycloaddition takes place by the reaction of acrylonitrile with diazoacetate to afford the oxazole derivative 27[29]. Bis(trimethylstannyl)diazomethane (28) undergoes Pd(0)-catalyzed rearrangement to give the A -stannylcarbodiimide 29 under mild conditions[30]. 

Other methods for the preparation of cyclohexanecarboxaldehyde include the catalytic hydrogenation of 3-cyclohexene-1-carboxaldehyde, available from the Diels-Alder reaction of butadiene and acrolein, the reduction of cyclohexanecarbonyl chloride by lithium tri-tcrt-butoxy-aluminum hydride,the reduction of iV,A -dimethylcyclohexane-carboxamide with lithium diethoxyaluminum hydride, and the oxidation of the methane-sulfonate of cyclohexylmethanol with dimethyl sulfoxide. The hydrolysis, with simultaneous decarboxylation and rearrangement, of glycidic esters derived from cyclohexanone gives cyclohexanecarboxaldehyde. 

Trifluoro- l-hydroxy-l-methylethyl)cyclohexene is monooxidized at both allylic positions in the nng with different agents. The major product is the rearranged product C when oxidation is accomphshed with chromiuin trioxide m methylene chlonde [42] (equation 34). 

Reaction of the morpholine or piperidine enamine of cyclopentanone, however, gives an unstable adduct which rearranges under the reaction conditions and an aqueous work-up to give the ring expanded ketone 2-chloro-2-cyclohexen-l-one (203) (138,139). 

Thermal decomposition gives olefins, probably by rearrangement of intermediate carbenes. For example, the decomposition of 3,3-penta-methylenediazirine (68) in nitrobenzene above 160°C gives cyclohexene [Eq, (58)]. The yield as determined by bromine titration... 

Examination of the reactions of a wide variety of olefins with TTN in methanol (92) has revealed that in the majority of cases oxidative rearrangement is the predominant reaction course (cf. cyclohexene, Scheme 9). Further examples are shown in Scheme 18, and the scope and limitations of this procedure for the oxidative rearrangement of various classes of simple olefins to aldehydes and ketones have been defined. From the experimental point of view these reactions are extremely simple, and most of them are... 

Allylic rearrangements with 3,3,6,6-dj-cyclohexene occurred in 20% of the MMO hydroxylation products compared to 33% for cytochrome P-450. These two experiments suggest that, with M. trichospor-ium OB3b, a rebound reaction must occur with a greater rate constant than with cytochrome P-450, in accord with the radical clock substrate work. 

Neier and coworkers have used a domino Diels-Alder/Ireland-Claisen process for the synthesis of (rac)-juvabione 4-46 and (rac)-epijuvabione [15]. Since neither the Diels-Alder reaction of the acetal 4-44 and methyl acrylate nor the sigmatropic rearrangement seemed to be stereoselective, these authors obtained the cyclohexene derivative 4-45 as a mixture of three diastereomers (Scheme 4.9). 

However, formation of an R species, either free or within a radical-pair cage with the metal (14), is strongly favored in view of the methylcyclopentane noted in the cyclohexen-4-al decarbonylation, since the rearrangement shown in eq. 5, metal-assisted if necessary, seems plausible (15) ... 

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