Trienes reactions

Azabicyclo[2.2.0]hexa-1,3,5-triene reactions, 7, 360 2-Azabicyclo[2.2.0]hex-5-ene reactivity, 7, 342 synthesis, 2, 371 2-Azabi cyclop. 1.0]hexene synthesis, 2, 371 2-Azabi cyclop. 1.0]hex-2-ene synthesis, 7, 67 2-Azabicyclo[k 1.0]hex-3-ene synthesis, 4, 258 6-Azabicyclo[k 1.0]hex-2-ene synthesis, 2, 305 Azabi cyclohexenes formation from azirines, 7, 58... 

Both the frontier-orbital and the Mobius-Hiickel methods can also be applied to the cyclohexadiene 1,3,5-triene reaction in either case the predicted result is that for the thermal process, only the disrotatory pathway is allowed, and for the... 

The pH dependence of the trien reaction indicates that no protons are added before the rate-determining step. Hence, this step cannot come after the peptide bond breaks, because the metal-free peptide group must add a proton. Thus, the subsequent displacement reactions of the donors in the first chelate ring occur after the rate-determining step, which agrees with the lack of methyl group effects in this ring. 

Cyclization of dienes and trienes. Reaction of a diene or triene with at least one terminal double bond with (CH3)3SnCl, AIBN, and NaBHsCN in r-BuOH results in addition of the ( 113)380 radical to the terminal double bond followed by cyclization to the other double bond. The C-Sn bond of the carbocycle is oxidatively cleaved by CAN in methanol to the dimethyl acetal of an aldehyde. This two-step synthesis provides a useful route to tetrahydrofurans and pyrrolidines as well as 1,6-dioxatriquinanes from allyl ethers. 

Irradiation of steroidal 3,7-dienes with ultraviolet light may result in ring opening and formation of various trienes. The most important reaction of this type is the conversion of ergosterol to previtamin Dj. 

Diene carboxylates can be prepared by the reaction of alkenyl halides with acrylates[34]. For example, pellitorine (30) is prepared by the reaction of I-heptenyl iodide (29) with an acrylate[35]. Enol triflates are reactive pseudo-halides derived from carbonyl compounds, and are utilized extensively for novel transformations. The 3,5-dien-3-ol triflate 31 derived from a 4,5-unsaturated 3-keto steroid is converted into the triene 32 by the reaction of methyl acrylate[36]. 

An active catalytic species in the dimerization reaction is Pd(0) complex, which forms the bis-7r-allylpalladium complex 3, The formation of 1,3,7-octa-triene (7) is understood by the elimination of/5-hydrogen from the intermediate complex 1 to give 4 and its reductive elimination. In telomer formation, a nucleophile reacts with butadiene to form the dimeric telomers in which the nucleophile is introduced mainly at the terminal position to form the 1-substituted 2,7-octadiene 5. As a minor product, the isomeric 3-substituted 1,7-octadiene 6 is formed[13,14]. The dimerization carried out in MeOD produces l-methoxy-6-deuterio-2,7-octadiene (10) as a main product 15]. This result suggests that the telomers are formed by the 1,6- and 3,6-additions of MeO and D to the intermediate complexes I and 2. 

Among several propargylic derivatives, the propargylic carbonates 3 were found to be the most reactive and they have been used most extensively because of their high reactivity[2,2a]. The allenylpalladium methoxide 4, formed as an intermediate in catalytic reactions of the methyl propargylic carbonate 3, undergoes two types of transformations. One is substitution of cr-bonded Pd. which proceeds by either insertion or transmetallation. The insertion of an alkene, for example, into the Pd—C cr-bond and elimination of/i-hydrogen affords the allenyl compound 5 (1.2,4-triene). Alkene and CO insertions are typical. The substitution of Pd methoxide with hard carbon nucleophiles or terminal alkynes in the presence of Cul takes place via transmetallation to yield the allenyl compound 6. By these reactions, various allenyl derivatives can be prepared. 

The alka-l,2,4-trienes (ailenylaikenes) 12 are prepared by the reaction of methyl propargyl carbonates with alkenes. Alkene insertion takes place into the Pd—C bond of the ailenyipailadium methoxide 4 as an intermediate and subsequent elimination of/3-hydrogen affords the 1,2,4-triene 12. The reaction proceeds rapidly under mild conditions in the presence of KBr. No reaction takes place in the absence of an alkali metal salt[4j. 

Organoboranes react with propargylic carbonates. Usually, addition of a base is essential for the Pd-catalyzed reactions of organoboranes, but the reaction with propargylic carbonates proceeds without addition of the base, because methoxide is generated in situ from carbonates. For example, the 1,2,4-triene 80 is prepared by the reaction of alkenylborane under neutral conditions[36]. 

The cyclization of the enediynes 110 in AcOH gives the cyclohexadiene derivative 114. The reaction starts by the insertion of the triple bond into Pd—H to give 111, followed by tandem insertion of the triple bond and two double bonds to yield the triene system 113, which is cyclized to give the cyclohexadiene system 114. Another possibility is the direct formation of 114 from 112 by endo-rype. insertion of an exo-methylene double bond[53]. The appropriately structured triyne 115 undergoes Pd-catalyzed cyclization to form an aromatic ring 116 in boiling MeCN, by repeating the intramolecular insertion three times. In this cyclization too, addition of AcOH (5 mol%) is essential to start the reaction[54]. 

Heteroatom functionalized terpene resins are also utilized in hot melt adhesive and ink appHcations. Diels-Alder reaction of terpenic dienes or trienes with acrylates, methacrylates, or other a, P-unsaturated esters of polyhydric alcohols has been shown to yield resins with superior pressure sensitive adhesive properties relative to petroleum and unmodified polyterpene resins (107). Limonene—phenol resins, produced by the BF etherate-catalyzed condensation of 1.4—2.0 moles of limonene with 1.0 mole of phenol have been shown to impart improved tack, elongation, and tensile strength to ethylene—vinyl acetate and ethylene—methyl acrylate-based hot melt adhesive systems (108). Terpene polyol ethers have been shown to be particularly effective tackifiers in pressure sensitive adhesive appHcations (109). 

Nylon 12 first beeame available on a semieommercial scale in 1963. The monomer, dodecanelactam, is prepared from butadiene by a multistaged reaction. In one proeess butadiene is treated with a Ziegler-type eatalyst system to yield the cyclic trimer, cyclododeca-1, 5, 9-triene. This may then be hydrogenated to give cyelododeeane, which is then subjeeted to direct air oxidation to give a mixture of cyclododecanol and cyclododecanone. Treatment of the mixture with... 

Electrocyclic reactions of 1,3,5-trienes lead to 1,3-cyclohexadienes. These ring closures also exhibit a high degree of stereospecificity. The ring closure is normally the favored reaction in this case, because the cyclic compound, which has six a bonds and two IT bonds, is thermodynamically more stable than the triene, which has five a and three ir bonds. The stereospecificity is illustrated with octatrienes 3 and 4. ,Z, -2,4,6-Octatriene (3) cyclizes only to cw-5,6-dimethyl-l,3-cyclohexadiene, whereas the , Z,Z-2,4,6-octa-triene (4) leads exclusively to the trans cyclohexadiene isomer. A point of particular importance regarding the stereochemistry of this reaction is that the groups at the termini of the triene system rotate in the opposite sense during the cyclization process. This mode... 

Reduction of the sodium salt of equilenin 17-ethylene ketal with lithium, sodium or potassium in ammonia at —70° occurs predominantly in the B-ring, affording, after acid hydrolysis, equilin (29) in up to 76% yield (55% isolated). The preferential reduction of the B-ring reflects the relative, but not absolute, resistance to reduction conferred on the A-ring by the naphthoxide ion. Some A-ring reduction does compete kinetically with B-ring reduction, since the epimeric 3-hydroxyestra-5,7,9-trien-17-ones are the major reaction by-products. Simple phenoxide ions usually reduce slowly... 

This reaction is especially well suited for the reduction of tertiary aldehydes which have no activated a-hydrogens. In this case only two deuteriums are incorporated in place of the carbonyl oxygen. The reduction of 12-methoxypodocarpa-8,ll,13-trien-17-al (82) provides an illustrative example. After back exchange of the aromatic deuteriums, the isotopic purity of the resulting dideuterio reduction product (83) is 92%. ... 

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