Methyl allene

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. 

Other isomerization products of excited methylenecyclopropane were butadiene, methyl allene, dimethyl acetylene, and ethylacetylene. The rate of isomerization of excited methylallene was slow compared to that of excited methylenecyclopropane. 

BUTADIENE. [CAS 106-90-0]. CHrCH C CH3, 1,3-butadiene (methyl-allene), formula weight 54.09. bp —4.41cC, sp gr 0.6272, insoluble in H2 O. soluble in alcohol and edier in all proportions, Butadiene is a very reactive compound, arising from its conjugated double-bond structure. Most butadiene production goes into die manufacture of polymers, notably SBR (styrene-butadiene rubber) and ABS (acryloiiitrile-buladiene-slyrene) plastics. Several organic syntheses, such as Diels-Alder reaction, commence with the double-bond system provided by this compound. 

Other less drastic reactions lead to methyl allene and cyclobutene. 

These results with 1,2-cyclononadiene make possible reassessment of some other stereochemical results. In reactions of racemic allenes or partially resolved allenes 38-51>, when will the rates of R + S reactions be significantly different from R + R or 5 + S dimerizations, and how will these rate differences influence the observed product distributions Even for optically inactive allenes, a serious uncertainty remains when many products are obtained, does this result from intermediates which lose their stereochemical bearings, or may it not be a consequence of many completely stereoselective paths being kinetically competitive Methyl-allene, for instance, has ten discrete modes of approach as two of these... 

In Scheme 63, four further examples of 1,5-diazocines obtained from 1,3-propanediamine derivatives are outlined, although only one was reported in good yields. Thus, iV-(2-aminoethyl)-l,3-propanediamine reacted with methyl allene dicarboxylate to give the diazepinodiazocine 79 in which the double bond can be located either on the diazocine ring or in the diazepine nucleus <1995H(41)1709>. 

The allenes, RC=C=CR, are readily prepared by this method from tetrahalides and dihalo olefins. Typical procedures are given for methyl-allene (72%) and 1-phenyl-l,2-butadiene (77%). A convenient route to the allenes from allyl halides is as follows ... 

Elimination of dialkyl phosphates from enol phosphates 30 (equation 91) with NaNH, in liquid ammonia proceeds readily and in high yields. Acetylenes are obtained when R is an aryl group (equation 91) however, when R is benzyl or methyl, allenes are the reaction products ". 

During a recent approach to the synthesis of the antibiotic polyoxins, methyl allene was treated with the N-sulfonyl imine from ethyl glyoxylate at 130°C [89] [Eq. (61)]. However, the desired [2+ 2]-cycloadducts 262 - 264 were obtained in only very small amounts, while imino ene product 261 was the major product, formed in 33% yield. 

The rate of the reaction decreases with increasing number of substituents in the acetylenic halide, and it is higher with acetylenic bromides than with the corresponding chlorides. Methyl magnesium iodide gives equal amounts of 1,1- and 1,3--substitution products, whereas tert.-butylmagnesium bromide does not react. However, for some tert.-butyl substituted allenes there exists an attractive com-... 

Oxidative cleavage of the complex 549 with CuCri affords 2,3-bis(chloro-methyl)-1,3-butadiene (550) and regenerates PdCri. Thus the preparation of this interesting dimerization product 550 can be carried out with a catalytic amount of PdCl2 and two equivalents of CuCb in MeCN[495], Similarly, treatment of allene with PdBr2 affords the dimeric complex 551. Treatment of this complex with 2 equiv, of bromine yields the dibromide 552. The tetra-bromide 553 is obtained by the reaction of an excess of bromine[496]. Similarly,... 

The catalytic oxidative carbonylation of allene with PdCb and CuCh in MeOH affords methyl a-methoxymethacrylate (559)[499]. The intramolecular oxidative aminocarbonylation of the 6-aminoallene 560 affords the unsaturated J-amino ester 561. The reaction has been applied to the enantioselective synthesis of pumiliotoxin (562)[500]. A similar intramolecular oxycarbonyla-tion of 6-hydroxyallenes affords 2-(2-tetrahydrofuranyl)acrylates[501]. 

Allenes also react with aryl and alkenyl halides, or triflates, and the 7r-allyl-palladium intermediates are trapped with carbon nucleophiles. The formation of 283 with malonate is an example[186]. The steroid skeleton 287 has been constructed by two-step reactions of allene with the enol trillate 284, followed by trapping with 2-methyl-l,3-cyclopentanedione (285) to give 286[187]. The inter- and intramolecular reactions of dimethyl 2,3-butenylmalonate (288) with iodobenzene afford the 3-cyclopentenedicarboxylate 289 as a main product) 188]. 

Like butadiene, allene undergoes dimerization and addition of nucleophiles to give 1-substituted 3-methyl-2-methylene-3-butenyl compounds. Dimerization-hydration of allene is catalyzed by Pd(0) in the presence of CO2 to give 3-methyl-2-methylene-3-buten-l-ol (1). An addition reaction with. MleOH proceeds without CO2 to give 2-methyl-4-methoxy-3-inethylene-1-butene (2)[1]. Similarly, piperidine reacts with allene to give the dimeric amine 3, and the reaction of malonate affords 4 in good yields. Pd(0) coordinated by maleic anhydride (MA) IS used as a catalyst[2]. 

Addition of arylhydroxylamines to electrophilic allenes such as methyl propadienoate or l-methancsulfonyl-l,2-propadiene is another route to 0-vinyl derivatives[2]. The addition step is carried out by forming the salt of the hydroxylamine using NaH and the addition is catalysed with LiO CCFj. The intermediate adducts are cyclized by warming in formic acid. Yields are typically 80% or better. 

A symmetric rotor must have either a C axis with n>2 (see Section 4.1.1) or an 54 axis (see Section 4.1.4). Methyl iodide has a C3 axis and benzene a Ce axis and, therefore, these are symmetric rotors whereas allene, shown in Figure 4.3(d), is also a symmetric rotor since it has an 54 axis which is the a axis allene is a prolate symmetric rotor. 

Other approaches to (36) make use of (37, R = CH ) and reaction with a tributylstannyl allene (60) or 3-siloxypentadiene (61). A chemicoen2ymatic synthesis for both thienamycia (2) and 1 -methyl analogues starts from the chiral monoester (38), derived by enzymatic hydrolysis of the dimethyl ester, and proceeding by way of the P-lactam (39, R = H or CH ) (62,63). (3)-Methyl-3-hydroxy-2-methylpropanoate [80657-57-4] (40), C H qO, has also been used as starting material for (36) (64), whereas 1,3-dipolar cycloaddition of a chiral nitrone with a crotonate ester affords the oxa2ohdine (41) which again can be converted to a suitable P-lactam precursor (65). 

Allene (prodiene) [463-49-0] M 40.1, m -146 , b -32 . Frozen in liquid nitrogen, evacuated, then thawed out. This cycle was repeated several times, then the allene was frozen in a methyl cyclohexane-liquid nitrogen bath and pumped for some time. Also purified by HPLC. [Cripps and Kiefer Org Synth 42 12 1962.]... 

Similarly alkylation (55) of l-N-pyrrolidino-2-methyl-l-propene (22) with propargyl bromide gave initial N alkylation to (23) with subsequent rearrangement to the allene (24). 

Reaction of lithiated allene with methoxymethyl isothiocyanate afforded 107, after trapping with methyl iodide. The newly formed 107 isomerizes under mild conditions to triene 108. This compound is ideally setup to experience an electrocyclization to dihydropyridine 109. Heating in the presence of acid facilitates aromatization of 109 to pyridines 110. 

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