Cumulenic ethers

Note 2. In view of the sensitivity of cumulenic ethers to oxygen the work up was carried out under nitrogen with water that had been saturated with ni trogen. 

The reaction of lithiated cumulenic ethers with ethylene oxide, trimethyl-chlorosilane and carbonyl compounds shows the same regiosnecificity as does the alkylation. 

As indicated in the general scheme below, butatrienes are the first products from base-induced 1,4-elinination of hydrogen and a suitable leaving group. The butatriene in general very readily undergoes isomerization into enynes, if sufficiently "acidic" protons are available (see Chapter 11 in Ref. 3a). In aprotic media cumulenic ethers are fixed as their lithio derivatives if an excess of alkyllithium is applied... 

Cumulenic ethers with the 4-positions blocked by alkyl groups can be obtained from bis-ethers, R0-CH2C=C-C(R )(r2)0R, and sodium amide in liquid NHj, applying the... 

Note 3. Cumulenic ethers are extremely oxygen-sensitive all operations during the work-up must be carried out under nitrogen. 

Note 7. Butyllithium in hexane can be used in principle, but the yield is lower because during the evaporation of the hexane some of the cumulenic ether is entrained. 

Note 2. In connection with the oxygen-sensivity of cumulenic ethers the work-up... 

Note 1. Because of the extreme sensivity of the cumulenic ether towards oxygen,... 

To a solution of 0.25 mol of the trimethylsilyl ether in 120 ml of dry diethyl ether was added in 20 min at -35°C 0.50 mol of ethyllithium in about 400 ml of diethyl ether (see Chapter II, Exp. 1). After an additional 30 min at -30°C the reaction mixture was poured into a solution of 40 g of ammonium chloride in 300 ml of water. After shaking, the upper layer was separated off and dried over magnesium sulfate and the aqueous layer was extracted twice with diethyl ether. The ethereal solution of the cumulenic ether was concentrated in a water-pump vacuum and the residue carefully distilled through a 30-cm Vigreux column at 1 mmHg. The product passed over at about 55°C, had 1.5118, and was obtained in a yield of 874. Distillation at water-pump pressure (b.p. 72°C/I5 mmHg) gave some losses due to polymerization. 

After the air in the flask had been replaced completely with nitrogen, 100 ml of dry diethyl ether, 0.20 mol of the cumulenic ether (see Chapter V, Exps. 7, 8 and 11) and 1 g (note 1) of copper(l) bromide were placed in it. A solution of the Grignard-reagent, prepared from 0.50 mol of the chloride (see Chapter II,... 

Analogous -substitutions take place when cumulenic ethers anti Grignard compounds are allowed. to interact in the presence of catalytic quantities of cqpper(I) salts. Organocopper compounds are the presumed intermediates [163,164]. 

Enyne ethers HC=CCH=CHOR are useful synthetic intermediates. They can be prepared by base-catalysed addition of alcohols to diacetylene. The required conditions are rather forcing and not very attractive for laboratory scale preparations. A much more convenient way to prepare the enyne ethers (in these cases more than 80 rel.% of the -isomer is obtained) consists in treatment of the easily accessible 1,4-dialkoxy-2-alkynes with two equivalents of alkali amide in liquid ammonia. The first step in this elimination is the (transient) formation of an "anion RO-fiH-C CCH OR, which eliminates ROH (143). The resulting cumulenic ether ROCH=C=C=CH2 is immediately converted into the metallaied enyne ether. 

Other methods reported to give conjugated enynes (144) include the ready addition of Grignard reagents to cumulenic ethers (143) in the presence of small amounts (10 mole %) of copper(l) bromide,the tra 5-addition of organo-aluminium hydrides to disubstituted diynes to give tran -enynes (145), and the... 

Cumulenic ethers with the 4-positions blocked by alkyl groups can be obtained from... 

During the final stage of the distillation, water from the bath was poured along the column in order to minimize the hold-up. Most of the product passed over between 25 and 40°C/15 mniHg. After cooling to room temperature nitrogen was admitted to the distillation apparatus. The cumulenic ether, n 1.5127, was obtained in 76% yield. 

Note 2. Commercial butyllithium in hexane as solvent or butylllthium in diethyl ether, prepared from butyl bromide and lithium, can also be used in principle, but we prefer to use ethyllithium because hexane is not easily separable from the rather volatile cumulenic ether and during the reaction of butyl bromide with lithium some octane is formed which cannot be separated from ethoxybutatriene. 

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