2-methyl-1-butene, addition

Addition of Grignard reagents to 1,2 epoxy-3-butene givw mixture of alcohols, MethylmagueBium bromide, for example gives 2-penten-l-ol as the principal product, together with some 2-methyl- -buten l-ol (Eq. 837). The former can he regarded as a... 

The methyl radical produced in primary Reaction 2 can abstract a hydrogen atom from an unreacted butene molecule in a chain propagation step or it can add to a butene molecule to provide a pentyl radical, which is the precursor for the observed Cr, products (see Reactions 7 and 8). Methyl radical addition (Reaction 8) is favored at low conversion... 

The methylvinyl radical (IV) can abstract a hydrogen atom from a feed or product molecule to form propylene or it can lose a hydrogen atom to form allene or propadiene as products. For the 2-butenes, steric factors inhibit methyl radical addition thus C5 products are formed to a far lesser extent than from 1-butene. While ethylene may be formed by a sequential decomposition of propylene, this cannot be the only path for its formation, as the yield of ethylene in the high conversion region increases about twice as rapidly as does the methane yield. An additional source of ethylene is the symmetrical cleavage of butadiene to vinyl radicals. 

This radical decomposes to give 2-methyl-l-butene plus a methyl radical. The resulting methyl radical can then enter into the noimial chain propagation sequence, or add to the parent molecule. As in the case of hydrogen atom addition, methyl radical addition gives predominantly tertiary radical adducts, 2,3-dimethyl-... 

From Table 2, it can be seen that atactic polypropylene (PP) and atactic poly(1-butene) (PB) exhibit C values of 6.0 and 5.6, respectively. As expected from the above cited RIS results, these values are considerably smaller than the Ctj, value for PE of ca. 8. The decrease in C is slightly greater for ethyl versus methyl substituents. Additional comparisons of RIS predictions and experimental results for PP and PB will be presented below. 

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]. 

Our belief that carbocations are intermediates m the addition of hydrogen halides to alkenes is strengthened by the fact that rearrangements sometimes occur For example the reaction of hydrogen chloride with 3 methyl 1 butene is expected to produce 2 chloro 3 methylbutane Instead a mixture of 2 chloro 3 methylbutane and 2 chloro 2 methylbutane results... 

Bromination of isoprene using Br2 at —5 ° C in chloroform yields only /n j -l,4-dibromo-2-methyl-2-butene (59). Dry hydrogen chloride reacts with one-third excess of isoprene at —15 ° C to form the 1,2-addition product, 2-chloro-2-methyl-3-butene (60). When an equimolar amount of HCl is used, the principal product is the 1,4-addition product, l-chloro-3-methyl-2-butene (61). The mechanism of addition is essentially all 1,2 with a subsequent isomerization step which is catalyzed by HCl and is responsible for the formation of the 1,4-product (60). The 3,4-product, 3-bromo-2-methyl-1-butene, is obtained by the reaction of isoprene with 50% HBr in the presence of cuprous bromide (59). Isoprene reacts with the reactive halogen of 3-chlorocyclopentene (62). 

Isoprene reacts with a-chloroalkyl ethers in the presence of ZnCl in diethyl ether from 0—10°C. For example,a-chloromethyl methyl ether at 10°C gives a 6 1 ratio of the 1,4-adduct, (F)4-chloro-l-methoxy-2-methyl-2-butene, to the 1,2-adduct, 2-chloro-l-methoxy-2-methyl-3-butene. Other a-chloroalkyl ethers react in a similar manner to give predominately the 1,4-addition product. A wide variety of aHyUc chlorides and bromides and a-chloroethers and esters add primarily 1,4- to isoprene in the presence of acid catalysts (8). 

In laser-impulse experiments with chlorophenyldiazirine the carbene could be observed by UV spectroscopy. On addition of defined amounts of alkene the rate of cyclopropanation was measured directly. The rate constants with various alkenes were (lO moF s ) 1-hexene, 1.3 ( )-2-pentene, 34 2-methyl-2-butene, 77 2,3-dimethyl-2-butene, 130 (80JA7576>. 

Further substitution can introduce additional factors, especially nonbonded repulsions, which influence conformational equilibria. For example, methyl substitution at C—2, as in 2-methyl-l-butene, introduces a methyl-methyl gauche interaction in the conformation analogous to B, with the result that in 2-methyl-l-butene the two eclipsed conformations are of approximately equal energy. Increasing the si2e of the group at... 

Among the cases in which this type of kinetics have been observed are the addition of hydrogen chloride to 2-methyl-1-butene, 2-methyl-2-butene, 1-mefliylcyclopentene, and cyclohexene. The addition of hydrogen bromide to cyclopentene also follows a third-order rate expression. The transition state associated with the third-order rate expression involves proton transfer to the alkene from one hydrogen halide molecule and capture of the halide ion from the second ... 

The regiochemistry is determined by the regiochemistry of the fluoride ion addition reaction, that is, via the most stable perfluorocarbanion intermediate Von Werner used a similar reaction to prepare silver compounds from perfluoro-2-methyl-2-butene and perfluoro 2 methyl-2-pentene [271] Silver(I) fluoride adds to bis(ttitluoromethyl)ketene in DMF without fluoride ion catalysis [270] The analogous trifluorovinylsulfurpentafluoride reacts similarly to give the isolable pentafluorosulfur derivative [272] (equation 187)... 

Fluoride ion produced from the nucleophilic addition-elimination reactions of fluoroolefins can cataly7e isomerizations and rearrangements The reaction of per fluoro-3-methyl-l-butene with dimethylamine gives as products 1-/V,/Vdimeth-ylamino-1,1,2,2,4,4,4-heptafluoro-3-trifluoromethylbutane, N,W-dimetliyl-2,2,4,4,4-pentafluoro 3 trifluoromethylbutyramide, and approximately 3% of an unidentified olefin [10] The butylamide results from hydrolysis of the observed tertiary amine, and thus they share a common intermediate, l-Al,A -dimethylamino-l,l 24 44-hexafluoro-3-trifluoromethyl-2-butene, the product from the initial addition-elimination reaction (equation 4) The expected product from simple addition was not found... 

Carbocations initially formed upon addition of an electrophile to an alkene may be able to undergo skeletal rearrangement depending on whether or not a more stable cation exists and, if it does exist, whether or not it can be reached via a low-energy pathway. Consider addition of HBr to 3-methyl-1-butene, the product of which is 2-methyl-2-butyl bromide. 

Draw Lewis structures for the possible carbocations resulting from protonation of the double bond in 3-methyl-1-butene, and decide which is favored. (Check your result using available energy data for C5H11 carbocations.) What would be the product of bromide addition to the more stable cation Is this the observed product ... 

What evidence is there to support the carbocation mechanism proposed for the electrophilic addition reaction of alkenes One of the best pieces of evidence was discovered during the 1930s by F. C. Whitmore of the Pennsylvania State University, who found that structural rearrangements often occur during the reaction of HX with an alkene. For example, reaction of HC1 with 3-methyl-1-butene yields a substantial amount of 2-chloro-2-methylbutane in addition to the "expected" product, 2-chloro-3-methylbutane. 

Perhaps the most striking difference between conjugated and nonconjugated dienes is that conjugated dienes undergo an addition reaction with alkenes to yield substituted cyclohexene products. For example, 1,3-butadiene and 3-buten-2-one give 3-cycIohexenyl methyl ketone. 

Of the 1,2-addition products, explain why 3,4-dibromo-3-methyl-hbutene (21%) predominates over 3,4-dibromo-2-methyl-l-butene (3%). 

The formation of optically active acyloins is also catalyzed by the yeast Candida Pareri if the bacteria Zymomonas mobilis and Zymomonas carlbergensis42 and the fungus Diplodia gossypina43. The latter microorganism produces (3/ ,66 )-6-hydroxy-7-oxo-8-norcitronellene from (/ )-citronellene by a reaction sequence that converts (7d)-citronellene to (/ )-4-methyl-5-butenal followed by addition of the acetyl moiety to the / e-face of the aldehyde. 

Lithiated (E)- and (Z)-l-(diphenylphosphinyl)-2-methyl-2-butenes undergo 1,4-addition to 2-cyclopentenone to mainly (E)-syn- and ( )-a /-adducts respectively2. 

The addition of the anions of racemic cyclic allylic sulfoxides to various substituted 2-cyclopentenones gives y-l,4-adducts as single diastereomeric products22. The modest yields were due to competing proton-transfer reactions between the anion and enone. The stereochemical sense of these reactions is identical to that for the 1,4-addition reaction of (Z)-l-(/erf-butylsulfinyl)-2-methyl-2-butene to 2-cyclopentenone described earlier. 

The application of auxiliary control in the asymmetric Michael addition of chiral enolates derived from ketones is rare the only example known is the use of (27 ,37 )-2,3-butancdiol as an auxiliary. The ketal of (27 ,37 )-2,3-butanediol with 3-methyl-l,2-cyclohexanedione reacts with 3-buten-2-one using as base a catalytic amount of sodium ethoxide in ethanol195. 

Similar additions may be performed with the enamine 13. However, with 3-buten-2-one or methyl 2-propenoate Lewis acid catalysis is needed to activate the Michael acceptor chloro-trimethylsilane proved to be best suited for this purpose. A remarkable solvent effect is seen in these reactions. A change from THF to HMPA/toluene (1 1) results in a reversal of the absolute configuration of the product 14, presumably due to a ligand effect of HMPA235. 

Chinchona alkaloids, such as quinine, are readily available quinuclidine chiral bases which have been used extensively in catalytic Michael additions239 243. Methy 1-2,3-dihydro-1-oxo-l/f-in-dene-2-carboxylate (1) is most frequently used as the Michael donor in these studies. Enantiose-lectivities as high as 76% are reached in the additions to 3-buten-2-one. Modest enantioselec-tivities (< 67%) were also obtained with ethyl 2-oxo-l-cyclohexanecarboxylate and methyl l,3-dihydto-3-oxo-l-isobcnzol urancarboxylate244 245. 

The highest enantioselectivities in the base-catalyzed Michael additions have so far been obtained using achiral bases complexed to chiral crown ethers. The addition of methyl 2,3-dihydro-l-oxo-1//-indene-2-carboxylate (1) to 3-buten-2-one using 4 mol% of a [l,T-binaphthalcnc]-2,2 -diol derived optically active crown ether 3 in combination with potassium AY/-butoxide as the base illustrates this successful method 259 260 It is assumed that the actual Michael donor is the potassium enolate complex of 1 and crown ether 3. 

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