Cumulene

CONVERSION OF ACETYLENES AND CUMULENES INTO ANIONIC AND ORGANOHETALLIC INTERMEDIATES... 

ACIDITY OF ACETYLENES AND CUMULENES AND STABILITY OE THEIR ANIONS... 

One of the most versatile methods for the synthesis of derivatives with the acetylene or cumulene system consists In deprotonatlon of the starting acetylene or cumulene and subsequent reaction of the anionic or organometal1ic intermediate with an electrophilic reagent. 

The stability of the various cumulenic anions depends to a large extent upon the nature of the groups linked to the cumulenic system. Whereas solutions of lithiated allenic ethers and sulfides in diethyl ether or THF can be kept for a limited period at about O C, the lithiated hydrocarbons LiCH=C=CH-R are transformed into the isomeric lithium acetylides at temperatures above about -20 C, probably via HC C-C(Li )R R Lithiated 1,2,4-trienes, LiCH=C=C-C=C-, are... 

Cumulenic anions, C=C=C and C=C=C=C, without strongly electron-withdrawing substituents are much stronger bases than acetylides, "CsC- and are therefore also stronger nucleophiles. In view of the poor stability of the cumulenic anions at normal temperatures this is a fortunate circumstance the usual functionalization reactions such as alkylation, trimethylsilylation and carboxylation in most cases proceed at a sufficient rate at low temperatures, provided that the... 

The reaction of cumulenic anions with electrophiles in principle may give two products ... 

Although several experimental data concerning the functionalization of cumulenic anions are availab. a (for a review see Ref. 10) (Table I), it remains difficult to predict the compos tion of the product of a particular reaction on a rationalistic basis. Especially the outcome of reactions with carbonyl compounds seems to be... 

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. 

BASE-PROMOTED INTERCONVERSIONS BETWEEN ACETYLENES AND CUMULENES 1. ISOMERIZATIONS WITH CATALYTIC AMOUNTS OF BASE... 

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... 

Treatment of geminal dihalocyclopropyl compounds with a strong base such as butyl lithium has been for several years the most versatile method for cumulenes. The dihalo compounds are easily obtained by addition of dihalocarbenes to double--bond systems If the dihalocyclopropanes are reacted at low temperatures with alkyllithium, a cyclopropane carbenoid is formed, which in general decomposes above -40 to -50°C to afford the cumulene. Although at present a number of alternative methods are available , the above-mentioned synthesis is the only suitable one for cyclic cumulenes [e.g. 1,2-cyclononadiene and 1,2,3-cyclodecatriene] and substituted non-cyclic cumulenes [e.g. (CH3)2C=C=C=C(CH3)2]. 

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. 

Note 1. In view of the strong foaming, a 500-ml distillation flask should be used. Note 2. Traces of oxygen cause polymerization of the cumulene and all operations... 

Apparatus 1-1 flask with a dropping funnel, a gas-tight mechanical stirrer and a very efficient reflux condenser the top of the condenser was connected with a trap. A tube containing anhydrous CaCl2 was placed between the trap and the water pump. The connection of the trap was made in such a way that the cumulene vapour could enter the large annular space (the long inner tube being connected to the water pump). 

Note 2. Traces of oxygen will induce polymerization of the cumulene. The NMR tube must therefore be filled with nitrogen before putting the sample in it. Low-temperature NMR gives the most representative results. 

In the flask were succesively placed 0.10 mol of the sulfinate (note 2), 25 ml of dry, pure HMPT (note 3), 4 g of powdered sodium iodide, 40 g of zinc dust and some boiling stones. After swirling for a few seconds the flask was connected with the other parts of the distillation apparatus, the system was evacuated immediately by means of the water pump (note 4) and the flask was then heated cautiously (free flame). A vigorous reaction started suddenly and the cumulene and part of the HMPT passed over. When the distillation had stopped completely... 

Vote 3. If more HMPT is used the yield of the cumulene will be lower the compound can remain longer in the hot reaction mixture, where it can polymerize. Mote 4. It is essential to follow the instructions given. The reaction sometimes starts very soon if in such a case the desired pressure (10-20 mmHg) has not yet been achieved, part of the cumulene may polymerize in the hot reaction mixture. 

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,... 

Chemistry of Ketenes, Allenes and Related Compounds", S. Patai (ed.), John Wiley and Sons, Chichester, New York, Brisbane, Toronto, (1980). lOe. H. Hopf, "The Preparation of Allenes and Cumulenes", Chapter 20 in "The Chemistry of Ketenes, Allenes and Related Compounds", S. Patai (ed.), John Wiley and Sons, Chichester, New York, Brisbane, Toronto, (1980). 

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