Tert-Butylallene

Note 1. The lithiation of monoalky1al 1 enes is not completely regiospecific. The ratio of a- to ylithiated allene varies from about 80 20 for methyl-allene to 93 7 for hexylallene. tert.-Butylallene, however, is metallated exclusively on the terminal carbon atom. 

A solution of (CH3)3C-CH=C=CLi, obtained by addition at -60°C of 0.20 mol of tert.-butylallene (see Chapter VI, Exp. 2) to a solution of 0.25 mol of ethyllithium in about 200 ml of diethyl ether (see Chapter II, Exp. 1) was warmed to 25°C and held at this temperature for 15 min. Subsequently the solution was cooled to below 0°C and 50 ml of saturated NH,C1 solution were added dropwise with vigorous stirring, keeping the temperature below 2o C. The upper layer v as separated off and the aqueous layer was extracted twice with 25-ml portions of diethyl ether. The combined solutions were dried over a small amount of magnesium sulfate. Slow distillation through a 40-cm Widmer column gave neopentyl acetylene (b.p. 76°C/750 mmHg, 20... 

The comparatively low yield of the initial dimerization of allene is also caused by further addition of 1 to 126 and other allene oligomers produced subsequently in the pyrolysis. A reinvestigation of the reaction has revealed that not only are new tetramers such as 287 and 288 formed in the reaction, but also numerous hexamers such as 289-292, the latter certainly not giving an indication that it originates from 1 [119]. Since some of these products still contain conjugated diene subunits - see, e.g., 291 - further growth appears likely tert-butylallene behaves similarly [120]. 

The [2 + 2]-cycloaddition reactions of l,3-di-tert-butylallene-l,3-dicarbonitrile (go) with imines afford azetidines [60]. The nitrogen atom of the imine was attached to the central carbon atom of the allene to give 2-methyleneazetidines. 

The reaction appears to be general as many allenes of different structures have been resolved by this method 202 204. The enantiomeric purities increase in the following order 1,3-dimethylallene < 1,2-cyclononadiene < 1,3-di-tert-butylallene < 1,3-di-ethylallene < 1,3-di-n-propylallene. 

Tert. butyl-4,4-dimethyl-penta-l,2-diene 1,1-di-tert. butylallene) (67) PE Spectrum 358. 

The "distillation" was stopped when the temperature in the top of the column had reached 55-60 C. Redistillation of the contents of the receiver through a 40-cm Midmer column gave tert.-butylallene, b.p. 79-82 C/7S0 mmHg, n 1.4196, in 77-84 yield (note 2). 

Solvolysis can also occur from the diazonium salts derived from the intermediate diazocy-clopropanes. Ring opening of cyclopropyldiazonium salts accounts for the solvolysis products in Table 2, entries 8 and 9. Evidence for this is seen when sodium methoxide is replaced by the weaker base, sodium hydrogen carbonate, in which case only the methyl ethers derived from methanolysis were obtained. The a-elimination reaction of 1-cyclopropyl-1-nitrosourea with base likely involves diazocyclopropanes as intermediates which readily eliminate molecular nitrogen to form cyclopropylidenes. A more direct approach to diazocyclopropanes involves the Bamford-Stevens route via tosylhydrazones. Thus di-/er/-butylallene (19) was prepared from the tosylhydrazone of ( )-2,3-di-tert-butylcyclopropanone on treatment with base. ... 

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