3-methyl-l,3-pentadiene

Interestingly, benzonitrile oxide does not react with thiirene dioxide 19b even in boiling benzene, whereas the electron-rich diene l-piperidino-2-methyl-l, 3-pentadiene (177) does react under the same reaction conditions to give the expected six-membered [4 + 2] cycloadduct 178, accompanied by sulfur dioxide extrusion and 1,3-hydrogen shift to form the conjugated system 179175 (equation 70). 

In one example, the Tics of the non-crystalline methyl, methine and methylene carbons of iPP, 70% crystalline, were compared at room temperature with those of model atactic poly(propylene), hydrogenated poly(2-methyl-l,3-pentadiene) [163]. It was found that, within the experimental error, the Tic values of each of the carbons were the same in both polymers. The conclusion can then be reached that the fast segmental motion, at or near the Larmor frequency of... 

Investigations on a series of miktoarm-star AB copolymers of PS and poly(2-methyl-l,3-pentadiene), PS(P2MP)3, indicate a different morphological behaviour [113] (Fig. 37), as predicted by Milner s theory [111] (Fig. 38). The discrepancies near the boundaries between different morphologies when compared with corresponding PS/PI systems on the one hand and to theoret-... 

Complexes 17-19 can be written in one valence structure as a, /3-unsaturated carbonyl compounds in which the carbonyl oxygen atom is coordinated to a BF2(OR) Lewis acid. The C=C double bonds of such organic systems are activated toward certain reactions, like Diels-Alder additions, and complexes 17-19 show similar chemistry. Complexes 17 and 18 undergo Diels-Alder additions with isoprene, 2,3-dimethyl-1,3-butadiene, tram-2-methyl-l,3-pentadiene, and cyclopentadiene to give Diels-Alder products 20-23 as shown in Scheme 1 for complex 17 (32). Compounds 20-23 are prepared in crude product yields of 75-98% and are isolated as analytically pure solids in yields of 16-66%. The X-ray structure of the isoprene product 20 has been determined and the ORTEP diagram (shown in Fig. 3) reveals the regiochemistry of the Diels-Alder addition. The C-14=C-15 double bond distance is 1.327(4) A, and the... 

The formation of the same cyclopropylamine from 2-methyl-l,3-pentadiene as from 4-methyl-l,3-pentadiene (entries 2 and 3 in Table 11.11) can most probably be attributed to initial isomerization of the former to the latter under the conditions employed. The fact that the conjugated 6-methyl-l,3,5-heptatriene yields only the 2,3-dialkenylcyclopro-... 

The reactions of 521 with 1,3-dienes were found to proceed exclusively in an [8 + 2] addition mode. The reactions were completely site and regioselective, as exemplified by the reaction between 521 and 2-methyl-l,3-pentadiene (525) which gave 526 after loss of CO2 (equation 152). The regiochemistry observed was in agreement with the frontier orbital coefficients calculated with semi-empirical methods. 

A catalytic asymmetric Diels-Alder reaction was developed by using 3-(3-borylpropenoyl)oxazolidin-2-ones 146. In the reactions of butadiene, isoprene, or 2-methyl-l,3-pentadiene and 146, in the presence of a chiral titanium catalyst 147, the cyclohexene derivatives 148 were formed. 

Although almost all kinds of thiocarbonyl compounds are good dienophiles, synthetic applications derived from the Diels-Alder adducts of thioketones, thionesters and dithioesters remain rather rare and focused on specific targets, as in the preparation of a fragment of the antibiotic erythronolide from the cycloadduct formed regioselectively from 2-methyl-l,3-pentadiene and an a-oxodithioester, a particularly efficient dienophile [524]. 

The addition of HBr to 2-methyl-l,3-pentadiene, 1-bromo-1,3-butadiene, 1-phenyl-1,3-butadiene and 2,4-hexadiene produces 2,4-dibromo-2-methylpentane, 1,3-dibromo-l-butene, 3-bromo-l-phenyl-1-... 

A European patent granted to Quest International Services BV involves use of pyridine derivatives as fragrance materials. 2-Alkyl-substituted pyridines are specifically mentioned, including all possible stereoisomers of 2-(2,4-dimethylcyclohexyl)pyridine 46, which is made from 2-vinylpyridine and 2-methyl-l,3-pentadiene via the Diels-Alder reaction <2006EP01562904>. 

Upon UV irradiation in hydrocarbon solution, the hexacarbonyls of chromium, molybdenum, and tungsten react differently with conjugated dienes like 1,3-butadiene (la), ( )-l,3-pentadiene (lb), 2-methyl-1,3-butadiene (lc), ( , )-2,4-hexadiene (Id), ( )-2-methyl-l,3-pentadiene (le), 2-ethyl-1,3-butadiene (If), or 1,3-cyclohexadiene (Ig). Chromium hexacarbonyl (2) yields, with the acyclic dienes la-lf, tetracarbonyl-r/2-dienechromium(0) complexes (3a-3f) in a smooth reaction (8-10). With 1,3-cyclohexadiene, in addition to 3g, dicarbonylbis(>/4-l,3-cyclohexadiene)chromium(0) (4g) is obtained [Eqs. (7) and (8)j. During chromatography on silica gel, the 1,3-cyclohexadiene complex 3g dismutates readily to [Cr(CO)6] and 4g [Eq. (9)]. Under the same conditions with 2 1,3-cyclopentadiene (lh) yields, in a hydrogen-transfer reaction, the stable dicarbonyl- / 5-cyclopentadienyl-r/ 3-cyclopent-enylchromium (5) (11-13) [Eq. (10)]. 

Monomers such as E-l,3-pentadiene (piperylene) and E-2-methyl-l,3-pentadiene give 1,4-polymers with an asymmetric carbon atom. Therefore, these monomers in principle will result in polymers with an isotactic, syndio-tactic or atactic structure. 

Early studies on the homopolymerization of E-l,3-pentadiene yielded polymers with a high cis-1,4-content and an isotactic structure, whereas E-2-methyl-l,3-pentadiene resulted in a polymer with a mixed czs-1,4/transit-structure [487-492]. Investigations on the polymerization of E-1,3-pentadiene with the system NdN/TIBA/DEAC partially support these findings as a poly(l,3-pentadiene) with a cis- 1,4-threo-disyndiotactic structure was obtained [492]. A somewhat lower cis- 1,4-content of 70% was obtained when the polymerization of E-l,3-pentadiene was catalyzed by (CF3COO)2NdCl/TEA [493,494]. When 2,3-Dimethyl-1,3-butadiene is polymerized with the catalyst NdN/TIBA/EtAlC the resulting poly(2,3-dimethyl-butadiene) predominantly contains cis-1,4-units [495,496]. 

A study on the homo- and copolymerization of a variety of dienes such as 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, E-l,3-pentadiene, E-l,3-hexadiene, E-l,3-heptadiene, E-l,3-octadiene, E,E-2,4-hexadiene, E-2-methyl-l,3-pentadiene, 1,3-cyclohexadiene mainly focused on mechanistic aspects [139]. It was shown that 1,4-disubstituted butadienes yield frans-1,4-polymers, whereas 2,3-disubstituted butadienes mainly resulted in cis- 1,4-polymers. Polymers obtained by the polymerization of 1,3-disubstituted butadienes showed a mixed trans-1,4/cis-1,4 structure (60/40). The microstructures of the investigated polymers are summarized in Table 26. 

In later studies on the homopolymerization of E-l,3-pentadiene with NdO/ TIBA/DEAC crystalline polymers with cis- 1,4-contents in the range 84-99% and a high isotacticity were obtained. It was found that the cis- 1,4-content increases when the polymerization temperature is decreased from room temperature to -30°C. The polymerization of E-2-methyl-l,3-pentadiene resulted in polymers which almost exclusively comprised cis- 1,4-units and no dependence of the cis- 1,4-content on polymerization temperature was observed. The obtained poly(2-methyl-l,3-pentadiene) was composed of various polymer fractions with different stereo regularities [165,166]. 

As was found for the polymerization of styrene, CpTiCT/M AO and similar half-sandwich titanocenes are active catalysts for the polymerization of conjugated 1,3 dienes (Table XX) (275). Butadiene, 1,3-pentadiene, 2-methyl-l,3-pentadiene, and 2,3-dimethylbutadiene yield polymers with different cis-1,4, trans-1,4, and 1,2 structures, depending on the polymerization temperature. A change in the stereospecificity as a function of polymerization temperature was observed by Ricci et al. (276). At 20°C, polypen-tadiene with mainly ds-1,4 structures was obtained, whereas at -20°C a crystalline, 1,2- syndiotactic polymer was produced. This temperature effect is attributed to a change in the mode of coordination of the monomer to the metallocene, which is mainly cis-rf at 20°C and trans-rj2 at -20°C. 

Fig. 3.5. Relationship between log (retention time) and boiling point for a range of hydrocarbons on squalane at 43°C. A, aliphatics (and benzene) B, alicyclics, 1-4 = C5-Cg n-alkanes 5 = 2-methyl-butane 6 = 2-methylpentane 7 = 2,3-dimethylbutane 8-12 = C4-C8 1-olefins 13,15,17 = trans-(but-2-ene, pent-2-ene and hept-2-ene) 14,16,18 = e/s-(but-2-ene, pent-2-ene and hept-2-ene) 19 = 2-methylbut-l-ene 20 = 2-methylpent-l-ene 21 = 4-methylpent-l-ene 22 = 2-methylbut-2-ene 23 = cyclopentane 24 = cyclohexane 25 = methylcyclopentane 26 = methylcyclohexane 27 = cyclo-pentene 28 = cyclohexene 29 = 4-methylcyclohexane 30 = 1,3-butadiene 31, 32 = trans- and cis-1,3-pentadiene 33 = diallyl 34, 35 = trans- and c s-2-methyl-l,3-pentadiene 36 = cyclopentadiene ...

As found for the polymerization of styrene, CpTiCl3/MAO and similar half-sandwich titanocenes are active catalysts for the polymerization of conjugated 1,3-dienes (Table 25) [218], Butadiene, 1,3-pentadiene, 2-methyl-l,3-pentadiene and 2,3-dimethylbutadiene yield polymers with different... 

Interestingly, this result contrasts with the reported photooxygenation of acyclic 1,3-dienes46. For example, 2-methyl-l,3-pentadiene leads to the Diels-Alder product, 3,5-dimethyl-3,6-di-hydro-1,2-dioxin, in 58% yield462. 

Bulk polymerization of frons-2-methyl-l,3-pentadiene lead only to i,4-trans addition polymer, however it allows randomization of the trans structure, leading to an atactic polymer. The polymerization of the clathrate of fr(Ms-2-methyl-l,3-pentadiene yielded an isotactic l, 4-trans addition polymer. The polymer formed from the bulk had a molecular weight of 20,000 (240 monomer units), and that formed from the clathrate had a molecular weight of lOOO (l2 monomer units). Similar results were obtained for other dienes, and the results are summarized in Table 4. it can be concluded that polymerization of dienes in the clathrate lead exclusively to a i,4-trans addition polymer, except in the case of 1,3-cyclohexadiene. For this monomer, although the polymer is formed entirely by 1,4-addition, the polymer formed is essentially atactic. In bulk polymerization, the polymerization proceeds in most cases through 1,4-addition (both trans and cis), but in the case of butadiene and 1,3-cyclohexadiene 1,2-additions were also observed. Actually, in the case of the bulk y-induced polymerization of 1,3-cyclohexadiene the 1,2-addition process was favoured over the 1,4-addition process by a ratio of 4 3. 

The electron-rich diene, 1 -piperidino-2-methyl-l,3-pentadiene (48), reacted with the thiirene 1,1-dioxide (31a) in boiling benzene to afford 61% of the dihydrobenzene derivative (50) via (49) (Scheme 21) <84JOC1300>. 

Diphenylthiirene dioxide (26a) was found to react with l-piperidino-2-methyl-l,3-pentadiene (27) to afford dihydrobenzene (28) in 61 % yield following loss of S02. Deamination with refluxing HC1 in ethanol gave the highly substituted benzene (29) quantitatively (Scheme 10) <84JOC1300>. Diels-Alder reaction between dimethylthiirene dioxide (26b) and (27) provided 1,2,3,5-tetramethylbenzene directly but in only 12% overall yield. 

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