Cycloheptadienes, from

A rare example of formation of cycloheptadiene from 1,3,8-triene was reported by Hiemstra et al. in the enantioselective synthesis of the tetracyclic left-hand substructure 301 of solanoeclepin A (302) (Scheme 1.55) [75]. Starting from compound 303, a [4-1-2]-cycloaddition was used to elaborate the oxabicyclic motif Nolan s catalyst [Ru]-VI (15 mol%) was used to cyclize the 1,3,8-triene 305 to the desired cycloheptadiene 306 in quantitative yield. It is worth mentioning that [Ru]-I was quite inefficient in this case even if a stoichiometric quantity was used. 

Diacetoxylation of various conjugated dienes including cyclic dienes has been extensively studied. 1,3-Cyclohexadiene was converted into a mixture of isomeric l,4-diacetoxy-2-cyclohexenes of unknown stereochemistry[303]. The stereoselective Pd-catalyzed 1,4-diacetoxylation of dienes is carried out in AcOH in the presence of LiOAc and /or LiCI and beiizoquinone[304.305]. In the presence of acetate ion and in the absence of chloride ion, /rau.v-diacetox-ylation occurs, whereas addition of a catalytic amount of LiCl changes the stereochemistry to cis addition. The coordination of a chloride ion to Pd makes the cis migration of the acetate from Pd impossible. From 1,3-cyclohexadiene, trans- and ci j-l,4-diacetoxy-2-cyclohexenes (346 and 347) can be prepared stereoselectively. For the 6-substituted 1,3-cycloheptadiene 348, a high diaster-eoselectivity is observed. The stereoselective cij-diacetoxylation of 5-carbo-methoxy-1,3-cyclohexadiene (349) has been applied to the synthesis of dl-shikimic acid (350). 

The hydrochloride of the crude ester obtained above was added to 25 ml of 2 N hydrochloric acid. The whole was kept under reflux for 2 hours. The material dissolved and a new hydrochloride then reprecipitated. After cooling, the hydrochloride of the crude acid was filtered off, washed with iced water and then recrystallized from distilled water. 5.7 g of 7-[dibenzo(a,d)cycloheptadien-6-yl] aminoheptanoic acid hydrochloride were obtained, melting instantaneously at 226° to 230°C. 

In the Supporting Information provided by Sinha et al., the formation of an unalike E/Z mixture of cycloheptadienes arising from 244d was presented... 

The preparation of N-carbethoxy-8-azabicyclo [5.1.0] oct-3-ene (158) from ethyl azidoformate (157) and 1,4-cycloheptadiene through a photolytic reaction, and its palladium(II)-catalyzed multistep rearrangement to N-carbethoxynortropidine (159), has been presented by Wiger and Retting as a new route to the 8-azabicyclo[3.2.1]octene skeleton (87) (Scheme 8). 

The parent system 20 was prepared from the 1,3-cycloheptadiene endoperoxide (Eq. 15) in 38% yield M,32). However, this double bond is quite sluggish towards saturation with diimide, so that a large excess of the diimide reagent is necessary, preferably recycling the incompletely reduced reaction mixture several times. 

An interesting application of a 1,2-disubstituted cyclopropanol in a seven-membered ring-annelation methodology has been developed by Cha et al. [82], The cyclopropanol 124, obtained from methyl 1-cyclopentenecarboxylate (123) and 4-(triisopropylsilyloxy)-butylmagnesium chloride, was converted to a 1,2-dialkenylcyclopropanol bis-silyl ether, which, by a subsequent facile Cope rearrangement, afforded the cycloheptadiene-anne-lated cyclopentane derivative 125 in 32% overall yield (Scheme 11.32). 

Recent advances in gas chromatographic separations of enantiomers allow precise determination of the enantiomeric purity of the algal pheromones. The czs-disubstituted cyclopentenes, such as multifidene, viridiene, and caudoxirene, are of high optical purity [ 95% enantiomeric excess (e.e.)] whenever they have been found (32,33). The situation is different with the cyclopropanes and the cycloheptadienes, as shown in Table 2 and Figure 1. Hormosirene from female gametes or thalli of... 

It was concluded from the formation of a dimer that 598 emerged by a DMS reaction in addition to a bicyclo[1.1.0]butane derivative [248]. The azacydoheptatetraene 599, trapped in an argon matrix kept at -261 °C, was observed by IR spectroscopy after photolysis of 3- and 4-diazomethylpyridine [249]. According to quantum-chemical calculations, the protodebromination of the respective bromodihydrodiazepi-nium ions is believed to proceed via the l,4-diaza-5,6-cycloheptadienes 600 and 601 as intermediates [169, 250],... 

Selenosulfonylation of olefins in the presence of boron trifluoride etherate produces chiefly or exclusively M products arising from a stereospecific anti addition, from which vinyl sulfones can be obtained by stereospecific oxidation-elimination with m-chloroper-benzoic acid134. When the reaction is carried out on conjugated dienes, with the exception of isoprene, M 1,2-addition products are generally formed selectively from which, through the above-reported oxidation-elimination procedure, 2-(phenylsulfonyl)-l,3-dienes may be prepared (equation 123)135. Interestingly, the selenosulfonylation of butadiene gives quantitatively the 1,4-adduct at room temperature, but selectively 1,2-adducts at 0°C. Furthermore, while the addition to cyclic 1,3-dienes, such as cyclohexadiene and cycloheptadiene, is completely anti stereospecific, the addition to 2,4-hexadienes is nonstereospecific and affords mixtures of erythro and threo isomers. For both (E,E)- and ( ,Z)-2,4-hexadienes, the threo isomer prevails if the reaction is carried out at room temperature. 

Non-heteroatom-substituted vinylcarbene complexes are readily available from alkynes and Fischer-type carbene complexes. These intermediates can undergo the inter- or intramolecular cyclopropanation reactions of non-activated alkenes. Cyclopropanation of 1,3-butadienes with these intermediates also leads to the formation of cycloheptadienes (Entry 4, Table 2.24). 

Cross-metathesis of terminal alkyne 142 and cyclopentene gives cyclic compound 143 having a diene moiety [Eq. (6.114)]. ° Terminal ruthenium carbene generated from an alkyne and methylidene ruthenium carbene complex reacts with cyclopentene to afford two-carbon elongated cycloheptadiene 143 ... 

Oxygenated dienes are exceptional substrates for vinylcarbenoids [78]. In order to avoid side-products derived from zwitterionic intermediates, nonpolar solvents are typically employed. A short synthesis of nezukone 57 highhghts the utiHty of the [3-1-4] cycloaddition for the synthesis of tropones (Scheme 14.4). The cycloaddition between the oxygenated butadiene 55 and 52 generates the cycloheptadiene 56 in 67% yield [78]. Treatment of 56 with Meli followed by acid-induced dehydration completes a very short synthesis of nezukone 57. 

Tropolones are readily accessible from the [3-1-4] cycloadditions of vinylcarbenoids with the highly oxygenated diene 58, as illustrated in Scheme 14.5 [79]. Treatment of the cyclic vinyldiazoacetate 59 with diene 58 in the presence of Rh2(OPiv)4 affords the fused cycloheptadiene product 60 in 68% yield. Deprotection followed by oxidation gives the single regioisomeric methyl tropolone 61 in 80% yield. 

Bis(cyclic) boronates derived from cycloheptadiene and cyclooctadiene are produced in good yields in a manner similar to that described in Section 10.21.9.2.4(i)(a) <1998JOC7322>. 

A combinatorial approach was applied to evaluate various catalysts for the animation of 1,3-dienes.594 Complexes formed from [(T 3-C3H5)PdCl]2 and PPh3 were the most active to induce the reaction of a broad range of primary and secondary ary-laminesand 1,3-cyclohexadiene, 1,3-cycloheptadiene, or 2,3-dimetyl-1,3-butadiene to give allylamines. The enantioselective version of the transformation is also very effective ... 

Intramolecular cyclopropanation using diazoesters is a powerful synthetic tool. Diazoesters are readily prepared from the corresponding alcohol via House s methods56-57. Numerous examples using the application of this transformation in synthesis have been reported. These include the potent synthetic pyrethroid NRDC 182 (22)58, (1 R)-( )-cis-chrysanthemic acid (23)59, the highly strained bicyclic system 2460, antheridic acid 2561,62 and cycloheptadiene 26 (equations 33-37). 

The photochemical behavior of cyclohexa-1,3-dienes113,114 differs from that of cycloheptadiene in that another pathway, that of ring opening, is available to the excited molecule in addition to the formation of the bicyclo[2.2.0]hexene system. This is reflected in the behavior of the corresponding heterocyclic derivatives. 

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