Ether, allenyl methyl

Living polymerization with the nickel catalyst enables the block copolymerization of alkoxyallenes [128]. The block copolymers from methoxyal-lene, ethoxyallene, butoxyallene, f-butoxyallene, and phenylallene have narrow molecular weight distributions regardless of the order of the addition of the two monomers. The copolymerization of hydrophilic diethylene glycol allenyl methyl ether and hydrophobic hexyloxyallene forms an amphiphilic block copolymer which is soluble in both water and hexane (Eq. 30). 

PEGA poly(ethylene glycol allenyl methyl ether)... 

Poly(Ethylene Glycol Allenyl Methyl Ether) (PEGA)... 

Allenyl Silyl enol ethers, 86 Allyl alcohol trimethylsilyl ether, 84 Allyl carbonates, 114-15 9 Allyl-ay 2 octalone, 34-5 2-Allyl-2 methylcyclohexanone, 106 (Allyldimethylsilyl)methyl chloride, 58, 59 (AUyldimethylsilyl)methylmagnesium chloride, 59... 

The addition of a-lithiomethoxyallene 144 [55] to benzaldehyde dimethylhydra-zone 145 (Eq. 13.48) leads to a mixture of pyrroline 146 and dihydroazete 147 [56]. The cydization in this case, which takes place in the same operation as the addition to the hydrazone, follows two distinct pathways, with attack of the nitrogen atom taking place at the inner, in addition to the terminal, carbon atom of the allene. A similar reaction of 144 with SAMP-hydrazone 148 (Eq. 13.49) leads to 3-pyrroline 149 in 88% yield and excellent diastereoselectivity [57]. Cleavage of the chiral auxiliary group from 149 takes place in two steps (1, methyl chloroformate 2, Raney nickel, 50 bar, 50 °C) in 74% overall yield. When the addition of 144 to 148 is conducted in diethyl ether, cydization of the adduct does not take place. Surprisingly, the hydrazones of aliphatic aldehydes react with 144 in poor yield in THF, but react quantitatively and diastereoselectively in diethyl ether to give the (uncyclized) allenyl hydrazone products. 

Mono- and di-alkylated furans were synthesized in a one-pot preparation from 2-propynyl-2-tetrahydropyranyl ether (106), butyllithium and formaldehyde. The intermediate allenyl ether (107) presumably cyclizes via a 2-(2-tetrapyranyloxy)-2,5-dihydrofuran (108) to afford the heterocycle (109) (79AG(E)875). In a similar manner, singly and doubly branched tetrahydropyranyloxybutynolates afforded the substituted furans (110) (Scheme 20). The thermocatalytic isomerization of ethyl l-methyl-2-phenylcyclopropene-3-carboxylate yielded the furan, possibly by a 1,3-sigmatropic displacement step or by a non-concerted biradical intermediate (75T2495). 

The addition of an allyl alcohol to racemic allenyl sulfoxides results in vinyl ethers with the sulfinyl moiety at C-1 that undergo sigmatropic rearrangements upon distillation to produce 2,4-dienones after ehmination of sulfenic acid. In one example, an isomeric vinyl ether was obtained with a sulfinyl methyl substituent at C-2 that gave rise to a sulfinyl enone upon rearrangement [138]. In related work, the addition-elimination of an allyl alkoxide to a functionalized vinyl sulfoxide results in a sulfinyl enol ether that rearranges with loss of sulfenic acid to the unsaturated ester [139-141] (Scheme 21). 

The anions generated from alkylamino carbene complexes can be alkylated in high yields with simple alkyl halides without any detectable amount of dialkylation. This is illustrated for the methyl pyiro-lidine complex (109), which can be alkylated cleanly with ethyl bromide to give the monoalkylated product (110) in 87% yield. The methyl pyrrolidine complex (109) can be prepared in nearly quantitative yield quite simply by treating an ether solution of the methyl methoxy complex (88a) with pyrrolidine at room temperature for a few minutes. A few examples of diastereoselective alkylations are known. The 0-alkylimidate carbene complex (112) can be alkylated with methyl triflate to give a 93 7 mixture of (113) and (114), which are diastereomers as a result of the chiral axis about the aza-allenyl linkage. Other examples of diastereoselective alkylations will be presented in Section 9.2.2.7. 

The conversion of a dimeric rr-bound methyl propargyl ether complex [Mo2(CO)4Cp2(At-Tj, i7--CH=CCH20Me)] (35) to the cationic allenyl complex [Mo2(CO)4Cp2(m-i7% i -CH=C=CH2] (36) has been described by Curtis et al. (25). Protonation of 35 with HBF4 induced the loss of methanol and formation of the required complex. Alternatively the same complex was reported accessible via the acid-promoted elimination of methanol from [Mo2(CO)4Cp2 M-T7%Tj -MeO(H)C=C=CH2 ], a rare example of an intact T7%Tj -bound allene (Scheme 9). 

Alkyl enol ethers can be conveniently prepared by the alkylation of a-methoxyvinyllithium and related metallated enol ethers. In a typical example, methyl vinyl ether (1) is converted by r-butyllithium to give a-methoxyvinyllithium (2). Reaction of (2) with octyl iodide gives the enol ether (3). Metallation of methyl propenyl ether (4) and methyl allenyl ether (5) can be similarly executed. ... 

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