Cycloaddition of cycloheptatriene

The bicyclo[4.4.1]undecane derivative 311 was obtained by [6+4] cycloaddition of 310 with a conjugated diene [72]. The [6+4] cycloaddition is a thermally allowed reaction, and free cycloheptatriene undergoes the [6+4] cycloaddition by heating. However, the [6+4] cycloaddition of cycloheptatriene coordinated by Cr(CO)3 proceeds at 0°C under irradiation. These results show the profound effect of coordination of Cr(CO)3 on reactivity. 

Cycloadditions. This system, (C H j.AICl/TiCU (20 1), induces 6 + 2] cycloaddition of cycloheptatriene with 1,3-butadiene, norbomadienes, and alkynes. 

The cobalt-mediated 6-I-2-cycloaddition of cycloheptatriene and allenes formed bicyclic cycloadducts in high yields and with an excellent E Z selectivity. Rh(I)- (g) catalysed formal intramolecular 6- -2-cycloaddition of the allenal (116) readily produced 5-8- and 6-8-fused bicyclic ketone cycloadducts (118) in excellent yields. A key intermediate in this cycloaddition is the rhodacycle (117) (Scheme 38). The TiCl4-Et2AlCl-catalysed 6-1-2-cycloaddition of 1,2-dienes and 1,3,5-cycloheptatrienes produced endo-bicyclo[4.2.1]nona-2,4-dienes in high yields (80%). ... 

Scheme 8.37 Rh-catalyzed [6-1-2] cycloaddition of cycloheptatriene and internal alkynes.

Clavier, H., Le Jeune, K., de Riggi, 1., Tenaglia, A., Buono, G. (2011). Highly selective cobalt-mediated [6-1-2] cycloaddition of cycloheptatriene and allenes. Organic Letters, 13, 308-311. 

Achard, M., Tenaglia, A., Buono,G. (2005). Firstcobalt(I)-catalyzed [6+2] cycloadditions of cycloheptatriene with alkynes. Organic Letters, 7, 2353-2356. 

SCHEME 19 A novel periselective cycloaddition of cycloheptatriene with cyclohexa-2,4-dienones. 

Singh, V. and Porinchu, M., A novel periselective cycloaddition of cycloheptatriene with cyclohexa-2,4-dienones, Tetrahedron iMt., 34, 2817,1993. 

The reaction of troponephenylhydrazone with carbon disulphide afforded the bicyclic thiazole (37) in quantitative yield. iV-methoxytroponimine when treated with phenylisothiocyanate afforded a mixture of cycloheptatriene derivatives (38a) and (38b). Both of these reactions proceed via an [8+2] cycloaddition <95H1675>. 

The metal-mediated and metal-catalyzed [6 + 2]- and [6 + 4]-cycloaddition reactions, pioneered by Pettit and co-workers105 106 and Kreiter and co-workers,107 respectively, involve the cycloaddition of metal-complexed cyclic trienes with 7r-systems such as alkenes, alkynes, and dienes. The [6 + 2]-reactions produce bicyclo[4.2.1]nonadiene derivatives and the [6 + 4]-reactions produce bicyclo[4.4.1]undecatrienes (Scheme 32). Trienes complexed to chromium, which can be prepared on large scale (40 g) as reported by Rigby and co-workers,108 react with 7r-systems upon thermolysis or irradiation.109-111 Chromium and iron-catalyzed [6 + 2]-reactions of cycloheptatrienes and disubstituted alkynes... 

Although disubstituted alkynes are used successfully as two-carbon components in chromium-mediated and -catalyzed [6 + 2]-reactions, the use of terminal alkynes produces a [6 + 2 + 2]-reaction (Section 10.13.3.7). Buono and co-workers have discovered that when a cobalt catalyst is employed, several monosubstituted alkynes can be used in [6 + 2]-cycloadditions with cycloheptatriene (Scheme 35). The use of a chiral BINOL-phosphoramidite cobalt complex affords an enantioselective [6 + 2]-cycloaddition reaction (Equation (18)).121... 

The palladium-catalyzed trimethylenemethane reaction with tropanones was reported in 1987 by Trost and Seoane and is the first example of a [6 + 3]-cycloaddition.130 Chromium-mediated [6 + 3]-cycloadditions of two types have been described-one in which the chromium complex activates the six-carbon component and one in which the chromium complex activates the three-atom component. An example of the first type involves the reaction of a cycloheptatriene-Cr(CO)3 complex with azirines to give cyclic imines in moderate yields (Scheme 40).131... 

Thus [6+2] cycloaddition of alkene with complex 306, bearing an optically active side chain, under irradiation at room temperature afforded the bicyclic compound 307 in 98% de [73]. According to the Woodward-Hoffmann rule, the [6+2] cycloaddition proceeds by irradiation, and is thermally forbidden. However, the cycloheptatriene complex 308 underwent 1,5-hydride shift, followed by [6+2] cycloaddition by heating, to give the tricyclic compound 309 in 90% yield [74], The cycloaddition was applied to the synthesis of /f-cedrene [75]. 

The presence of the methoxycarbonyl substituent at C-7 affects the reaction course of the cycloaddition of diethyl diazenedicarboxylate to the cycloheptatriene moiety, since the ene product is not produced. A mixture of tropylidene- and norcaradiene-type adducts 8 and 9 is obtained, whose ratio is dependent on the temperature13. 4-Phenyl-3//-l,2,4-triazole-3,5(4//)-dione, however, affords the norcaradiene-type adducts 10 exclusively with 7-substituted cyclo-heptatrienes14"19. 

The thermally induced [6 + 4] cycloaddition of 2,4,6-cycloheptatrien-l-one (tropone) (1) with a variety of diene pikers has played a central role in the development of the mechanistic precepts and preparative utility of the entire class of higher-order pericyclic processes. The relatively well-defined reaction parameters for these cycloadditions render diem particularly well-suited for the rqiid assembly of relatively complex polycyclic carbon arrays. 

The thermal cycloaddition of phencyclone (85) with cycloheptatriene offers additional mechanistic insight into these reactions (Scheme 13). In this case a 57% yield of the corresponding endo [2 -i- 4] adduct was isolated. Further pyrolysis of this material at 170 C provided the decarbonylated pentacyclic material (86) along with an exo [6 h- 4] adduct (87). The course of this reaction can be contrasted with the thermolysis of compound (83). l ile neither of these examples is of great potential synthetic value, they do serve to illustrate some of the typical mechanistic themes which characterize these reactions. 

Site selectivity in a number of other concerted cycloadditions which are not [4 + 2] cycloadditions is also explained by frontier orbital control. Thus diphenylketene (332) reacts with isoprene (333) mostly at the more substituted double bond, and with cis-butadiene-l-nitrile (334) at the terminal double bond.263 Dichlorocarbene reacts at the terminal double bond of cycloheptatriene (335),264 and the Simmons-Smith reaction (336 + 337)265 also takes place at the site with the higher coefficients in the HOMO. 

Numerous examples for the synthesis of cyclopropanes by [2-f 1] cycloaddition of photochemically generated acylcarbenes to alkenes, allenes, 1,3-dienes, and cycloheptatriene are given in Houben-Weyl Vol. 4/5b, pp 1158-1257 and in Vol. E19b, pp 1099-1107 and pp 1300-1303. 

Photolysis of a-diazo esters in the presence of benzene or benzene derivatives often results in [2-1-1] cycloaddition of the intermediate acylcarbene to the aromatic ring, thus providing access to the norcaradiene (bicyclo[4.1.0]hepta-2,5-diene)/cyclohepta-l,3,5-triene valence equilibrium. The diverse effects that influence this equilibrium have been discussed (see Houben-Weyl, Vol. 4/3, p509). To summarize, the 7-monosubstituted systems obtained from a-diazoacetic esters exist completely in the cycloheptatriene form, whereas a number of 7,7-disubstituted compounds maintain a rapid valence equilibrium in solution. On the other hand, several stable 7-cyanonor-caradienes are known which have a second 7t-acceptor substituent at C7 (see Section 1.2.1.2.4.3). Subsequent photochemical isomerization reactions of the cycloheptatriene form may destroy the norcaradiene/cycloheptatriene valence equilibrium. Cyclopropanation of the aromatic ring often must compete with other reactions of the acylcarbene, such as insertion into an aromatic C H bond or in the benzylic C H bond of alkylbenzenes (Table 7). 

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