2.4- Dimethyl-l,3-pentadiene

A novel synthesis of an oxetane from a 1,4-diene by means of the new reagent PhSeOH has been reported. From 2,4-dimethyl-l,4-pentadiene there was obtained 2,4-dimethyl-2,4-bis(phenylselenomethyl)oxetane (65) in 34% yield. This compound can be deselenated with Raney nickel to 2,2,4,4-tetramethyloxetane (79JOC1742). 

For purposes of comparison it should be noted that very powerful metallating agents (e.g., butyllithium/TMEDA or butyllithium/potassium t-butoxide) are capable of abstracting two or even three protons from various alkylated dienes. Thus, various hexadienes and methyl pentadienes have been converted to dianionic species, while 2,4-dimethyl-l,4-pentadiene, 1,4-heptadiene, and 1,4-cycloheptadiene have all been converted to trianions84-86. ... 

The iS-oxide 400 undergoes ring-opening, presumably to the sulfenic acid 401, which cyclizes to five-membered products. The intermediate may be trapped by reaction with trimethylsilyl chloride it reacts with norbornene to give bis-norbornyl sulfoxide, probably via an elimination of 2,4-dimethyl-l,4-pentadien-3-one from an initial adduct. 

Vapor pressure osmometry in chloroform. Dlolefine = 2,5-dimethyl-l,5-hexadiene. DiolefinG = 2,4-dimethyl-l, 4-pentadiene. 

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]. 

Electron transfer sensitized irradiation of acyclic dienes gives rise to mixtures of [4 + 2] and [2 + 2] dimers for example, an 8 1 mixture was obtained from 2,4-dimethyl-l,3-pentadiene [137]. On the other hand, [4 + 2] dimers were obtained exclusively upon oxidation with aminium radical cation salts [138]. This difference has led some workers to question the key role of electron transfer in these reactions... 

The allylalkohol 6 turns out to be the obvious precursor of the protected diol 5, and 6 reasonably arises from a Shapiro coupling of cyclohexadienyllithium 7 with the cyclohexene-4-aldehyde 8 which is the product of oxidation and subsequent diol protection of the bicyclic hydroxylactone 9 the latter emerges from rearrangement of the Diels-Alder cycloadduct 13 of 3-hydroxy-2-pyrone 14 as the diene and 4-hydroxy-2-methyl-2-butenoate 15 as the electron-deficient dienophile. The cyclohexadienyllithium 7 originates from the sulfonylhydrazone of the ketone 10 which is, once again, a Diels-Alder cycloadduct of the protected 3-hydroxymethyl-2,4-dimethyl-l,3-pentadiene 12 and ketene 11 as the dienophile. 

Triblock copolymers can be synthesized by either the difiinc-tional initiator or the sequential monomer addition routes under ambient conditions such as room temperature polymerization conditions. Poly(benzyl methacrylate)-27-poly(lauryl methacrylate)- 7-poly(benzyl methacrylate) (PBzMA-PLMA-PBzMA) was synthesized using l,5-bis(trimethylsi-loxy)-1,5-dimethoxy-2,4-dimethyl- 1,4-pentadiene (BDDB)... 

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