Bicyclo heptadienes

Formation of the tricyclo[3.3.0.0.]decane 209 by the reaction of [3.2.0]bicyclo-heptadiene 205 with propyne complex (206) is an example [81], The Pauson Khand reaction is explained by the following simplified mechanism. At first the oxidative cyclization of 205 and 206 generates the cobaltacyclopentene 207, to which insertion of CO gives 208. Finally, reductive elimination of208 affords the cyclopentenone 209. 

Bicyclo[2.2.1]heptadiene rearranges at elevated temperatures to cycloheptatriene and toluene. The reaction is facilitated by substituents at C-7 such as phenyl and alkoxy, in which case cycloheptatrienes are the dominant products. 

Another application of catalyst 8 is to the reaction of acetylenic aldehydes [10c] (Scheme 1.18, Table 1.6). Two acetylenic dienophiles have been reacted with cyclo-pentadiene or cyclohexadiene to give bicyclo[2.2.1]heptadiene or bicyclo[2.2.2]octa-diene derivatives in high optical purity. A theoretical study suggests that this reaction proceeds via an exo transition state. 

Selektiv gelingt die Reduktion einer C=C-Doppelbindung mit Lithiumalanat im 7-Hydroxy-bicyclo[2.2.1]heptadien zum anti-7-Hydroxy-bicyclo[2.2.1]hepten (—100% d.Th.)3 ... 

The elimination of carbon monoxide can occur by a concerted process in some cyclic ketones. The elimination of carbon monoxide from bicyclo[2.2.1]heptadien-7-ones is very facile. In fact, generation of bicyclo[2.2.1]heptadien-7-ones is usually accompanied by spontaneous decarbonylation. 

Acyclic dienes as 1,6-heptadienes can be converted to bicyclic compounds, e.g. bicyclo[3.2.0]heptanes, in the presence of cuprous triflate (4.36) 439). 

Diisobutylaluminium hydride catalyses the ring-closure of various dienes. It is proposed that the process involves addition of the aluminium hydride to a terminal double bond, followed by ring-closure and, finally, elimination of the catalyst (equation 106). Thus 1,5-hexadiene gives methylenecyclopentane (213) (equation 107), 1,6-heptadiene gives methylenecyclohexane (214) (equation 108), 4-vinylcyclohexene gives bicyclo[3.2.1]oct-2-ene (215) (equation 109) and the spiro compound 217 is obtained from 5-methylene-l,8-nonadiene (216) (equation 110)112. 

The generation of bicyclo [2.2.1]-heptadiene-7-one is accompanied by the elimination of CO spontaneously... 

In the 7-azabicyclo[2.2.1]heptadiene series there is as yet no instance known of aromatization by deamination such as occurs with some naphthalen-l,4-imine and anthracen-9,10-imine derivatives (see Sections III, H and IV, D). On the other hand, a close parallel exists between those reactions and some instances of aromatization of bicyclo[2.2.1] structures by loss of a heavier heteroatom from the 7-position, e.g., 70 71. 1,2,3,4,5-Pentaphenylphosphole reacts with dimethyl acetyl-... 

Methyl 2-bromo-2-cyclopropylideneacetate (11a) has never been tested in these reactions, but has been used as a starting material for the stepwise construction of 1,6-heptadienes with methylenecyclopropane units for intramolecular Heck reactions. Thus, bromo ester 11a, after reduction, subsequent conversion of the resulting alcohol to the bromide and coupling with enolates of substituted malonates, was transformed into dienes of the type 254 (Scheme 73) - versatile synthetic blocks for the preparation of functionally substituted spirocyclopropanated bicyclo[4.3.0]nonenes 255a-d by a domino Heck-Diels-Alder reaction [122a]. 

Cl 209Ru2C22Hn Ruthenium(II), p-aqua-bis( A-trichloroacetato)bis[Ti4-bicyclo-[2.2.1]heptadiene) (trichloro-acetato)-, 26 256... 

Exercise 21-22 Unlike the conversion of bicyclo[2.1,0]-2-pentene to 1,3-cyclo-pentadiene, bicyclo[4.1.0]-2,4-heptadiene is transformed to 1,3,5-cycloheptatriene very rapidly at low temperatures by what appears to be a wholly concerted mechanism. Account for this difference. 

A direct entry to the quadricyclene series has been gained through photoisomerization of bicyclo [2.2.1 ]heptadienes. Bicyclo [2.2.1 ]hepta-dien-2,3-dicarboxylic acid (Formula 194), undergoes light-induced valence tautomerization to Formula 195 (75). The parent quadricyclene 196 has been prepared by direct irradiation of bicyclo [2.2. l]heptadiene... 

Bicyclo[2.2.1]heptadiene is converted to quadricyclene by direct irradiation (76) orbenzophenone-sensitizedirradiation (77) (seeSec. HE). 

In a bicyclo[4.1.0]heptadiene, there should be a walk-around rearrangement analogous to the one we discussed above in the bicyclic allylic cations.143... 

Hydrogenation of Complex 3 under similar conditions is very slow and it proved more convenient to generate the corresponding bicy-clo[2,2,l]heptadiene complex in situ from DiPAMP and bis-bicyclo-[2,2,l]heptadiene-rhodium[I]hexafluorophosphate. 

Interestingly, zirconacyclopentane 246 formed by the reaction of 1,6-heptadiene with the Zr complex has the firms ring junction mainly [108]. It should be noted that the preparation of the trans ring junction in the bicyclo[3.3.0]octane system by other means is difficult. Carbonylation of 246 affords trans-fuzed bicyclo[3.3.0]octanone 247 [109,111]. The diacetoxy compound 248 is obtained by oxidative cleavage of 246. Protonation affords the frans-dimethylcyclopentane skeleton. Similar reactions occur with 1,6-enynes, and Pauson Khand-type cyclopentenone synthesis is possible by carbonylation. 

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