Octa-l,6-dienes

Pinenes have also been used as feedstock to prepare several linear non-conjugated non-terpenic dienes (e.g. 3,7-dimethyl-l,6-octa-l,6-diene and 5,7-dimethylocta-l,6-diene) used in the synthesis of elastomeric ethylene-propylene-diene terpolymers [14]. 

The disulphide (130) was obtained by the reaction of myrcene (7-methyl-3-methylene-octa-l,6-diene) with sulphur. Carbon-13 n.m.r. spectra of 3-methyl-l,2-dithian and of the derived 1- and 2-monoxides, the 1,1- and... 

The result of oxidation of 8-hydroxy-2,3-tetrafluorobenzobicyclo[3 2 l]octa-2,6-diene depends on the configuration of the hydroxyl group In the syn isomer, the double bond is not epoxidized by the Jones reagent [5/] (equation 52)... 

C2PSi-C2N2Si-C6 5,8-Diaza-l-phospha-4-sila-benzo-spiro[3.4]octa-2,6-diene 6, 681/... 

C4Se-CsSe-C6-C6 8-Selena-2,6-dibenzo-bicyc lo[3.2. l]octa-2,6-diene 12, 492... 

The major product is l,4-dimethyl-4-vinylcyclohexene together with smaller amounts of 1,6-dimethylcyclo-octa-l,5-diene, isoprene and 4-isopropenyl-1 -methylcyclohexene. 

Experimental Procedure 3.2.6. Alkylidenation of a Ketone 4-Methyl-l-phenyl-octa-l,3-diene... 

Diazabicyclo[3,3,0]octa-2,6-dienes of type 391 undergo a sequence of electrocyclic reactions upon thermolysis and photolysis (82JPC338) to yield 4,5-diazaocta-l,3,5,7-tetraenes (393), probably via 392 (79CB2620). The influence of the substitution pattern on the conditions necessary for initiation of the reaction and on the valence isomeric equilibria have been studied (86JPC5552). 

Octan-l-ol acetate Rh Oct-trans-2-en-l-al Rh Octa-2-6-diene-l-8-diol, 2-6-dimethyl Rh Octa-3-7-diene-l-6-diol, 2-6-dimethyl Rh Octa-3-cis-6-dien-l-al, 3-7-dimethyl Rh Octa-d-tram-h dien-l-al, 3-7-dimethyl Rh Octa-traTiS 2 CiS 6 dien l ol, 3-7 dimethyl 8-hydroxy, P-D-glucopyranoside Rh 5.2 °... 

RhCl(PPh3)3] (23) and [RhCl(CO)(PPh3)2] (71) catalyze the formation of enol silyl ethers and derivatives according to equation (86). Both the (E) and (Z) isomers of the product are obtained.4353 The dinuclear complex [Rh2Cl2(CO)4] (96) catalyzes the reaction of phenylacetylene with carbon monoxide to give 3,6-diphenyl-l-oxabicyclo-[3.3.0]-octa-3,6-diene-2,4-dione (97) (equation 87).435b... 

Another type of bicyclo[3.3.0]octadienone formation is observed in the reactions of 4,4-gem-disubstituted 1,6-heptadiynes (353) with HSiMe2Bu-t catalyzed by Rh(acac)(CO)2 or Rh2Co2(CO)i2 under forced conditions, i.e. at 120 °C and 50 atm of CO, affording 7,7-disubstituted bicyclo[3.3.0]octa-l,5-dien-3-ones (354) in 71-95% isolated yields (equation 143)340,341. 

The reaction is catalyzed by Pd(0) complexes, but the pre-catalyst can be either a Pd(0) or a Pd(II) compound that is to be reduced in situ. Oxidative coupling of two butadienes coordinated to a Pd(0) species of the phosphine ligand (species A, Scheme 4) results in the formation of intermediate [Pd(l,2,3,8-r 4-octa-2,6-diene-l,8-diyl)(L)] (B). This oxidative coupling is rather facile and reversible the latter illustrated by the fact that B is only stable at high butadiene concentration. Subsequent protonation of B by NuH at the 6-position of the ri r -octadienyl ligand leads to [Pd(l,2,3,7,8-ri5-octa-2,7-dien-l-yl)(L)]Nu (C). The complex of type C is a pivotal intermediate as several reaction pathways are available from here. 

One classic example is an experiment reported by Doering and Roth in 196217 (Scheme 1.XIII). Upon heating, racemic 3,4-dimethylhexa-l,5-diene (13) rearranged to a mixture of (2 ,6 )-octa-2,6-diene (90%), (2Z,6Z)-octa-2,6-diene (9%), and a trace amount of (2 , 6Z)-isomer. The experimental results are explained in terms of a six-membered transition state17 (Scheme 1.XIV). Chairlike transition state A is favored over transition state B based on the conformational analysis of 1,2-dimethylcyclohexane, in which the methyl substituents prefer to be in an equatorial position. The observation that 14 Z was formed in only trace amounts indicates that boatlike transition state C is of significantly higher energy than transition state A or B. 

Scheme 3 Stepwise versus domino cross-coupling-cydoaddition reactions on 8-oxabi-cyclo[3.2.l]octa-2,6-dienes [22]...

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