Allenes preparation

Freshly distilled allene should be used. It should be free of 2-chloropropene, usually present in allene prepared by zinc dehalogenation of 2,3-dichloropropene,3 to avoid formation of chlorine-containing products that liberate hydrogen chloride on distillation. 

The palladium-catalyzed allene preparation method was extended to an asymmetric counterpart using a Pd/(R)-binap species as a chiral catalyst and axially chiral allenes 103 were obtained with good eantioselectivity [96]. It was found that the pres-... 

Allen prepared several 2-(rn-dialkylaminoalkoxy)-4-oxo-4/f-pyrido[l, 2-a]-pyrimidines by reacting the 3-substituted derivatives of 63 (R = H) with dialkylaminoalkyl halides.104 3-Substituted pyrido[l,2- ]pyrimidines (63 R = H) have also been treated with methyl iodide98 and methyl sulfate,278 but the structures of the products have not been elucidated. 

ONE-STEP HOMOLOGATION OF ACETYLENES TO ALLENES PREPARATION OF 4-HYDR0XYN0NA-1,2-DIENE (1,2-Nonadien-4-ol)... 

Dehalooenation Chromous chloride. Copper powder-Benzoic acid. Dimethyl sulfoxide-NaH. Hydrazine-Palladium. Iron pentacarbonyl. Lithium-l-Butanol-THF. Magnesium-Iodine-Ether. Methyllithium. Sodium acetate. Sodium iodide. Zinc dust. Zinc dust-Ethanol (see Allene, preparation. Hexafluoro-2-butyne, preparation). 

The other enyne-allenes prepared by Wang by this method are outlined in Scheme 24.21 [13]. 

Figure 15.30 Structure of the bent allene, bis(N,/V-climethylbenzimidazolyl)allene, prepared by Dyker etal. [159].

White crystals m.p. 162-164 C. ll can be prepared by the fermentation of sugar with the mould Aspergillus lerreus or by healing citra-conic anhydride with water at ISO C. Electrolysis of the potassium salt in solution gives allene. Itaconic acid is used as a comonomer in plastics its esters are polymerized to lubricating oils and plasticizers. 

L,2-propadiene, allene, CH2=C = CH2, CjH4. Colourless gas prepared by the electrolysis of potassium itaeonate, or by the action of zinc and alcohol on 1,3-dibromopropane. It is easily isomerized to propyne (methylacetyl-ene), and is produced as a mixture with this substance from some reactions. 

The lithiation of allene can also be carried out with ethyllithium or butyl-lithium in diethyl ether (prepared from the alkyl bromides), using THF as a cosolvent. The salt suspension which is initially present when the solution of alkyllithium is cooled to -50°C or lower has disappeared almost completely when the reaction between allene and alkyllithium is finished. 

The alkylations proceeded much more slowly, when ethyl- or butyllithium in diethyl ether, prepared from the alkyl bromides, had been used for the metallation of allene, in spite of the presence of THF and HMPT as co-solvents. 

Ojj 1.5068, was obtained in a yield of 82%. The equilibrium mixture obtained in the isomerization under the influence of KO-tert.-61,89 in DHSO consisted of about 70% of allene and 30% of yneamine. Base-catalysed isomerization is therefore not a suitable method to prepare the yneamCne. 

Apparatus 5-1 round-bottomed, wide-necked flask with a mechanical stirrer for the preparation of CH3CEC-S-tert.C9H9 1-1 round-bottomed flask and a rubber stopper, perforated by a glass tube of 4-5 mm I.D., connected to a plastic tube, for the conversion into the allenic sulfide. The glass tube extended to 2 mm from the bottom of the flask. 

Some allenic alcohols can be prepared in analogous waysfrom acetylenic epoxides or tetrahydropyrans ... 

A wide variety of compounds with the allene system has been prepared from the... 

Note 2. The reaction between CHjCu and HCsC-CH(CH3)OTs gave pure 2,3-pentadiene in about 70% yield, using the isolation procedure described above. This means that for the preparation of about 4 g of the allene about 16 g of CuBr and 250 ml of THF are required ... 

To a mixture of 100 ml of THF and 0.10 mol of the epoxide (note 1) was added 0.5 g Of copper(I) bromide. A solution of phenylmagnesium bromide (prepared from 0.18 mol of bromobenzene, see Chapter II, Exp. 5) in 130 ml of THF was added drop-wise in 20 min at 20-30°C. After an additional 30 min the black reaction mixture was hydrolysed with a solution of 2 g of NaCN or KCN and 20 g of ammonium chloride in 150 ml of water. The aqueous layer was extracted three times with diethyl ether. The combined organic solutions were washed with water and dried over magnesium sulfate. The residue obtained after concentration of the solution in a water-pump vacuum was distilled through a short column, giving the allenic alcohol, b.p. 100°C/0.2 mmHg, n. 1.5705, in 75% yield. 

Apparatus. 500-ml round-bottomed, three-necked flask with a gas inlet tube, thermometer and a gas outlet for the preparation of chlorotetrahydropyran 1-1 four--necked, round-bottomed flask with a gas inlet tube, a dropping funnel, a mechanical stirrer and a thermometer, combined with a gas outlet for the preparation of HC=CMgBr and its reaction with chlorotetrahydropyran 1-1 three-necked, round--bottomed flask with a dropping funnel, combined with a gas inlet, a mechanical Stirrer and a thermometer, combined with a gas outlet for the conversion into the allenic alcohol. 

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