Dimethyl-3,4-pentadienal

Unusual Pd-catalyzed fragmentation occurred in the reaction of 1-phenyl-2,2-dimethyl-3,4-pentadien-l-ol (395) with iodobenzene. The arylated diene 397 and benzaldehyde were obtained in high yields. In this reaction, phenylpalladium attacked the central carbon to generate the 7r-allylpalladium intermediate 396. Then decarbopalladation ( -carbon elimination) occurred to provide the arylated diene 397 and a-hydroxybenzylpalladium 398, which collapsed to benzaldehyde and Pd(0) [152]. 

Ethyl 3,4-pentadienoate, 203 - (S) Ethyl 3,4-hexadienoate, 204 - (0) 2,2-Dimethyl-3,4-pentadienal, 204 - (7) 3-Hethyl-l,2-butadienyl acetate (l-acetoxy-3-methyl-l,2-butadiene), 205... 

Analog wie Pentadien-(1,4) und Hcxadicn-(1,5) verhaltensich 2-Methyl- und 2,4-Dimethyl-pentadien-(l,4) bzw. 2-Methyl-hexadien-(l,5)1. 

Interestingly, controlled copolymerization was achieved in the isobutylene/2,4-dimethyl pentadiene-1,3 system, explained by the internal strain exerted by the methyl groups of the 2,4-dimethyl pentadiene-1,3 incorporated into the copol5uner, and the presence of electron-pair donors forming in situ from the initiators (190). 

A telomerization reaction of isoprene can be carried out by treatment with 2-chloro-3-pentene, prepared by the addition of dry HCl to 1,3-pentadiene (67). An equimolar amount of isoprene in dichi oromethane reacts with the 2-chloro-3-pentene at 10°C with stannic chloride as catalyst. l-Chloro-3,5-dimethyl-2,6-octadiene is obtained in 80% yield by 1,4-addition. 

Nonfluonnated allenes also readily react with fluoroalkenes to give diverse fluonnated alkylidenecyclobutanes [727, 12S, 129, 130] (equations 55 and 56), except for tetramelhylallene, which rearranges to 2,4-dimethyl 1,3-pentadiene under the reaction conditions prior to cycloaddition (equation 57) Systematic studies of l,l-dichloro-2,2-difluoroethylene additions to alkyl-substituted allenes establish a two-step, diradical process for alkylidenecyclobutane formation [131, 132, 133]... 

Paraformaldehyde, 40 1,3-Pentadiene, 3-bromo-2,4-dimethyl-, 35 1,3 Pentadicnc, 3-bromo 2-methyl-, 35... 

Pcntarncthoxy-benzaldehyd1 —> 4,5,5-Trichlor-2,3-dibrom-pentadien-(2,4)-aP — 7,7- Dimethyl-1-formyl-... 

Dermal Effects. Skin irritation was noted in wildlife officers at the RMA after they handled sick or dead ducks without gloves (NIOSH 1981). Although the investigators concluded that diisopropyl methylphosphonate contributed to the local effects, a number of other compounds were present. Analysis of the pond water indicated the presence of a number of organic and inorganic contaminants, including diisopropyl methylphosphonate (11.3 ppm) aldrin (0.368 ppm) dieldrin (0.0744 ppm) dicyclo-pentadiene, bicycloheptadiene, diethyl benzene, dimethyl disulfide, methyl acetate, methyl isobutyl ketone, toluene, and sodium (49,500 ppm) chloride (52,000 ppm) arsenic (1,470 ppm) potassium (180 ppm) fluoride (63 ppm) copper (2.4 ppm) and chromium (0.27 ppm). Because of the presence of numerous compounds, it is unclear whether diisopropyl methylphosphonate was related to the irritation. 

The photochemistry of l,l,5,5-tetraphenyl-3,3-dimethyl-l,4 pentadiene (1) has been studied in detail by Zimmerman and Mariano.<7) Photolysis of compound (1) gave 1,1-diphenyl-2,2-dimethyl-3-(2,2-diphenylvinyl) cyclopropane ... 

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... 

For the synthesis of permethric acid esters 16 from l,l-dichloro-4-methyl-l,3-pentadiene and of chrysanthemic acid esters from 2,5-dimethyl-2,4-hexadienes, it seems that the yields are less sensitive to the choice of the catalyst 72 77). It is evident, however, that Rh2(OOCCF3)4 is again less efficient than other rhodium acetates. The influence of the alkyl group of the diazoacetate on the yields is only marginal for the chrysanthemic acid esters, but the yield of permethric acid esters 16 varies in a catalyst-dependent non-predictable way when methyl, ethyl, n-butyl or f-butyl diazoacetate are used77). 

A striking example for the preferred formation of the thermodynamically less stable cyclopropane is furnished by the homoallylie halides 37, which are cyclopro-panated with high c/s-selectivity in the presence of copper chelate 3891 The cyclopropane can easily be converted into cw-permethric acid. In contrast, the direct synthesis of permethric esters by cyclopropanation of l,l-dichloro-4-methyl-l,3-pentadiene using the same catalyst produces the frans-permethric ester (trans-39) preferentially in a similar fashion, mainly trans-chrysanthemic ester (trans-40) was obtained when starting with 2,5-dimethyl-2,4-hexadiene 92). 

The change in selectivity is not credited to the catalyst alone In general, the bulkier the alkyl residue of the diazoacetate is, the more of the m-permethric acid ester results 77). Alternatively, cyclopropanation of 2,5-dimethyl-2,4-hexadiene instead of l,l-dichloro-4-methyl-l,3-pentadiene leads to a preference for the thermodynamically favored trans-chrysanthemic add ester for most eatalyst/alkyl diazoacetate combinations77 . The reasons for these discrepandes are not yet clear, the interplay between steric, electronic and lipophilic factors is considered to determine the stereochemical outcome of an individual reaction77 . This seems to be true also for the cyclopropanation of isoprene with different combinations of alkyl diazoacetates and rhodium catalysts77 . 

The products of electrochemical oxidation of conjugated dienes are considerably affected by the reaction conditions such as the material of the electrode, the supporting electrolyte and the solvent. The oxidation of butadiene with a graphite or carbon-cloth anode in 0.5 M methanolic solution of NaClCU mainly yields dimerized products along with small amounts of monomeric and trimeric compounds (equation 5)1. The use of platinum or glassy carbon mainly gives monomeric products. Other dienes such as isoprene, 1,3-cyclohexadiene, 2,4-hexadiene, 1,3-pentadiene and 2,3-dimethyl-l,3-butadiene yield complex mixtures of isomers of monomeric, dimeric and trimeric compounds, in which the dimeric products are the main products. 

In addition to styrene, Bottini and Hilton [84] employed 1,3-cyclopentadiene, (Z)-1,3-pentadiene and 2,3-dimethyl-l,3-butadiene to intercept 123, which was generated from 122. 1,3-Cyclopentadiene gave rise to three [4 + 2]-cycloadducts 126 (Scheme 6.30) and (Z)-l,3-pentadiene furnished mainly one [2 + 2]-cycloadduct 127. In the case of 2,3-dimethyl-l,3-butadiene, the major product was a mixture of three... 

Scheme 6.30 Structure ofthe trapping products of bicyclo[3.2.1]-octa-2,3-diene (123) with 1,3-cyclopentadiene, (Z)-l, 3-pentadiene and 2,3-dimethyl-l, 3-butadiene and ofthe dimers of123.

Dichlorination of tetramethylallene afforded 3-chloro-2,4-dimethyl-l,3-pentadiene as the single product, whereas the same reaction of 1,1-dimethylallene yielded a mixture of 2-chloro-3-methyl-l,3-butadiene, 2,3-dichloro-3-methyl-l-butene and 1,2-dichloro-3-methyl-2-butene, indicating the intermediacy of the 2-chloroallylic cationic intermediate 11 [13]. 

Tetramethoxypropadiene 88 or l-methoxy-l-(trimethylsilyl)-3-phenyl-l,2-pentadiene 89 may be easily protonated and then leads to dimethyl malonate or 1-tri-methylsilyl-3-phenyl-2-penten-l -one [42]. 

Dimerization of conjugated dienes and trienes is generally accomplished at elevated temperatures or in the presence of metal catalysts. Linear dimerization of butadiene occurs readily at room temperature on nickel catalysts bearing aminophosphinite (AMP) ligands, and the reaction rate is reportedly twice that observed in other nickel systems employing either morpholine, ethanol or P-methyloxaphospholidines as modifiers62. 1,3-Pentadiene dimerizes in the presence of 1 mol% nickel catalyst to give a diastereomeric mixture of 4,5-dimethyl-l,3,6-octatriene as shown in equation 42. 

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