N-Butylallene

Widmer column gave butylallene, b.p. 105 C/760 mmHg, n 1.4332. The remaining liquid was distilled in a partial vacuum (60-100 mmHg, b.p. 40-70°C) and the distillate was redistilled at normal pressure to give an additional amount of butylallene, bringing the yield to 72-78%. 

Widmer column gave fert.-butylallene, b.p. 79-82T/760 mmHg, njj 1.4196, in n- At yield (note 2). 

Metallation of allerns Allene is metallated at C, by n-butyllithium in THF at — 78°. In the absence of HMPT, the lithio derivative can be alkylated to give a 1-alkylallene (86-93% yield). Under the same conditions, a 1,1-dialkylallene is convertible into a pure 1,1,3-trialkylallene, but a 1-alkylallene is metallated at C, or C3, depending on the size of the alkyl group. When R contains more than four carbons, metallation is largely at C3. Metallation of 1,1,3-trisubstituted allenes requires t-butyllithium or n-butyllithium + 1 equiv. of HMPT 1,1 -dimethyl-3,3-di-w-butylallene can be prepared in this way in 86% yield. 

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. 

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). 

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