Cycloheptatriene synthesis

Cycloheptatrienes, synthesis of 801 Cyclohexadienes 800, 801 Cyclohexanols, synthesis of 838 Cyclopentanones, naturally occurring 321 Cyclopentanone sulphoxides, reactions of 341... 

Cycloheptatriene.—Synthesis. 7-Norbornadienol, available by saponification of 7-acetoxynorbornadiene, undergoes rapid base-catalysed rearrangement to the tropyl system. The mechanism suggested involves a 1,3-sigmatropic shift with inversion to... 

Cycloheptatriene.—Synthesis. Details have been published on the preparation of specifically substituted cycloheptatrienes by the cycloadditon of cyclopropenes to thiophene-1,1-dioxides followed by expulsion of S02. Substituted tropones have been obtained from the furan adducts of bromo-oxyallyl cations e.g. treatment of l,l,3,3-tetrabromo-4-methylpentan-2-one with di-iron nonacarbonyl in the presence of furan gave adduct (141) which was converted into a-thujaplicin (142). Acid hydrolysis of the norbornyl ketal (143) followed by warming to 70 "C gave 7,7-dimethyl-cycloheptatriene. ... 

Scheme 8.18 Cycloheptatriene synthesis through Pd-catalyzed co-cyclization of allylic alcohols and aUcynes.

Hilt, G., Paul, A., Hengst, C. (2009). Cobalt-catalysed [6+2] cycloaddition of internal alkynes and terminal alkenes with cycloheptatriene. Synthesis, 3305-3310. 

An interesting cycloheptatriene (182) synthesis has been described using thiophene 1, 1-dioxides (180) and cyclopropenes 181 (equation 121)ns. Concerted [4 + 2]cycloaddition and subsequent cheletropic extrusion of sulfur dioxide are suggested by the second-order kinetics (first in each reactant), and by the large negative activation entropy. 

A transmetalation of the styrylcarbene chromium complex 62 in the presence of stoichiometric amounts of [Ni(cod)2] to give the nickel carbene intermediate 63 was applied to the synthesis of Cr(CO)3-coordinated cycloheptatriene 64 upon reaction with terminal alkynes [57] (Scheme 37). The formation of pen-tacarbonyl(acetonitrile)chromium is expected to facilitate the metal exchange. 

Diazomalonic esters serve as intermediates for the synthesis of a wide variety of compounds including cyclopropanes, cyclo-propenes, cycloheptatrienes, sulfur ylides, lactones, and substituted malonates. ... 

With l,3>5-cycloheptatriene 2 can be trapped to yield four isomeric [2+2] adducts and the exo/endo isomeric [6+2] compound 16. Heating this mixture to 110°C leads to the complete transformation of the silacyclobutanes into 16 via a dipolar intermediate. The attempted synthesis of the diphenyl derivative of the [2+2] products leads to the stereospecific formation of endo-Yl which could be characterized by X-ray diffraction analysis [4]. 

Attempts to synthesize l,2-diazacycl[3.2.2]azines (l,2,4-triazolo)[3,4,5-ti/]indolizines, for example, 337, have met with very limited success. To date the ring system is known only when fused on its ef-faces to a cycloheptatriene ring (see Section 12.16.6.4). It may be that the 1,2-diazacyclazine system is more strained than that of the parent cyclazines, since the N-N bond of the triazole ring is expected to be shorter than a C-C or C-N bond. Similarly, all attempts to form the N-N bond as the final step in a synthesis of the 1,2,4-triazacyclazine ring system, 359, have been unsuccessful <1987J(P1)1159>. 

For cycloheptatriene and a series of its derivatives various thermal unimolecular processes, namely conformational ring inversions, valence tautomerism, [1,5]-hydrogen and [l,5]-carbon shifts, are known. An example of such multiple transformations was described65 which can provide a facile approach to new polycyclic structures by a one-step effective synthesis (yields up to 83%) of the two unique ketones 156 and 157. The thermolysis of the neat ether 151 at 200 °C for 24 h gives initially the isomeric allyl vinyl... 

The cycloheptatriene for this synthesis can be obtained best by thermal rearrangement of the Diels-Alder addition product of cyclopentadiene and ethyne ... 

The products formed in these reactions are very sensitive to the functionality on the carbenoid. A study of Schechter and coworkers132 using 2-diazo-1,3-indandione (152) nicely illustrates this point. The resulting carbenoid would be expected to be more electrophilic than the one generated from alkyl diazoacetate and consequently ihodium(II) acetate could be used as catalyst. The alkylation products (153) were formed in high yields without any evidence of cycloheptatrienes (Scheme 33). As can be seen in the case for anisole, the reaction was much more selective than the rhodium(II)-catalyzed decomposition of ethyl diazoacetate (Scheme 31), resulting in the exclusive formation of the para product. Application of this alkylation process to the synthesis of a novel p-quinodimethane has been reported.133 Similar alkylation products were formed when dimethyl diazomalonate was decomposed in the presence of aromatic systems, but as these earlier studies134 were carried out either photochemically or by copper catalysis, side reactions also occurred, as can be seen in the reaction with toluene (equation 36). 

This methodology has been applied to the synthesis of the bicyclic system (157),133 an advanced intermediate previously used in the synthesis of confertin.138 Reaction of the diazo compound (158) with rho-dium(II) mandelate gave an equilibrating mixture of the norcaradiene (159) and the fused cycloheptatriene (160) in essentially quantitative yield (Scheme 35). The mixture of (159) and (160) was converted to (157) in six steps in 20% overall yield. 

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]. 

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