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. 

To a solution of 0.50 tnol of ethyllithium in about 450 tnl of diethyl ether (see Chapter II, Exp. 1) was added 0.20 mol of 1-heptyne or butylallene (see Chapter VI, Exp. 1) with cooling below Q°C. After the addition the cooling bath was removed and the thermometer-gas outlet combination was replaced with a reflux condenser. The solution was heated under reflux for 6 h. The thermometer-gas outlet was again placed on the flask and the yellow suspension was cooled to -50°C. Trimethylchlorosilane (0.20 mol) was added dropwise in 10 min, while keeping the temperature between -40 and -35°C. After having kept the mixture for an additional 30 min at -30°C, it was poured into 200 ml of ice-water. The aqueous layer was extracted three times with small portions of diethyl ether. 

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... 

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). 

Butylallene, which fails to react with (PhSe)2 under palladium catalysis, undergoes the diselenide addition upon photo-irradiation (Equation (80)).215 Using the (PhS)2/(PhSe)2 binary system, introduction of two different chalcogen elements into allenic C=C bond is also viable (Equation (81)). 

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. 

A Ni(dppe)Br2-Zn system effectively catalyzes co-cydotrimerization of an allene with a propiolate. The reaction is highly regio- and chemoselective to afford a poly-substituted benzene derivative in good yield. (Scheme 16.82) [92], From the observation that no desired [2 + 2 + 2] product is obtained for the reaction of 1-hexyne and phenylacetylene with w-butylallene under similar conditions, the presence of an electron-withdrawing C02Me group in the alkyne moiety is essential for the success of the present [2 + 2 + 2]-co-cyclotrimerization. 

With the aid of 13C NMR, 6Li NMR and XH HOESY (heteronuclear Overhauser effect spectroscopy) NMR of a-lithiomethoxyallene (106) and l-lithio-l-ethoxy-3-J-butylallene (107) as well as by ab initio model calculations on monomeric and dimeric a-lithiohy-droxyallene, Schleyer and coworkers64 proved that 106 and 107 are dimeric in THF (106 forms a tetramer in diethyl ether) with a nonclassical 1,3-bridged structure. The 13C NMR spectrum of allenyllithium in THF is also in agreement with the allenic-type structure the chemical shift of C2 (196.4 ppm) resembles that of neutral allene (212.6 ppm), rather than C2 of propyne (82.4 ppm). 

FIGURE 52. Cl 13C NMR signal of 6Li-labeled 1-lithio-l-ethoxy-t-butylallene (107) in THF-ds at —92 °C. Reprinted with permission from Reference 64. Copyright (1994) American Chemical Society... 

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. 

Butenes, with propylene co-polymers, 4, 1075 -Butene zirconocenes, preparation, 4, 889 Butenyl polystyrene, as solid support, 12, 739 / r/-Butylallene, dichalcogenide additions, 10, 758 />-/ r/-Butylcalix[4]arenes... 

Di-f-butylallene oxide (64) is an isolable compound prepared by the oxidation of 1,3-di- -butylallene with m-chloroperbenzoic acid. Upon heating at 100 °C for 5 h, 50% of 64 is isomerized to trans-2,3-di-f-butylcyclopropanone (52).51> Likewise, oxidation of 1,1-di-f-butyl-allene (65) with buffered peracetic acid (equimolar quantities) affords 2,2-di-f-butylcyclopropanone (6(5).55a> Although the intermediate is presumably 3,3-di-f-butylallene oxide, it has not been detected. 

On the other hand, treatment of the mono-2-butylallene oxide 67 with one equivalent of peracid yields the spiro-Ws-epoxide 68 and the acetoxy ketone 69.55b> Similarly, the peracid oxidations of tetramethyl-allene, 1,1-dimethylallene, and 1,2-cyclononadiene do not give the... 

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. 

Classic work by Loftfield on the Favorskii reaction showed that cyclopropanones are intermediates in the base-induced rearrangement of a-haloketones (l heme 4). Isolation of such an intermediate was accomplished in the reaction of the sterically hindered a-bromodineopentyl ketone (9) with potassium p-chlorophenyldimethylcarbinolate. The identity of the product (10), rrans-2,3-di-t-butylcyclopropanone, was established by independent synthesis of 1,3-di-t-butylallene oxide (11) which underwent valence isomerization to (10) ... 

An interesting route to the cyclopropanone system involves the rearrangement of allene oxides, usually generated by the epoxidation of allenes. Thus, 1,3-di-t-butylallene oxide (11) may be prepared by the reaction of 1,3-di-t-butylallene with m-chloroperbenzoic acid. Heating 11 to 100 °C leads to isomerization, forming truns-2,3-di-t-butylcyclopropanone (10) (Scheme 4) Similarly, 1,1-di-t-butylallene (15) yields 2,2-di-t-butylcyclopropanone with peracetic acid (equation 7) ... 

Dehydration of allylic alcohols with strong acid leads to allenes if an isomerization to an alkyne is not possible. This method has been used for the synthesis of tetraarylallenes and tetra-r-butylallene. This method was also used for the first synthesis of an optically active allene by an enantioselective dehydration using (-l )-camphorsulfonic acid. ... 

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. ... 

Monoalkylallenes undergo smooth living polymerization promoted by the Ni complex to give the corresponding polyallenes with controlled molecular weights and narrow molecular weight distribution [123]. The polymers produced are composed of -C(=CH2)-CHR- units formed via 1,2-polymer-ization and -CH2-C(=CHR)- units via 2,3-polymerization in approximately 1 9 ratio. The polymerization of terf-butylallene and 1,1-dialkylallenes affords the corresponding polymers which contain the structural unit via... 

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