5.5- Dimethyl-l-hexene

Two approaches for the synthesis of allyl(alkyl)- and allyl(aryl)tin halides are thermolysis of halo(alkyl)tin ethers derived from tertiary homoallylic alcohols, and transmetalation of other allylstannanes. For example, dibutyl(-2-propenyl)tin chloride has been prepared by healing dibutyl(di-2-propenyl)stannane with dibutyltin dichloride42, and by thermolysis of mixtures of 2,3-dimethyl-5-hexen-3-ol or 2-methyl-4-penten-2-ol and tetrabutyl-l,3-dichlorodistannox-ane39. Alternatively dibutyltin dichloride and (dibutyl)(dimethoxy)tin were mixed to provide (dibutyl)(methoxy)tin chloride which was heated with 2,2,3-trimethyl-5-hexen-3-ol40. 

For propylene dimerization, four products can be written (Table II) if only vinylic C—H bonds are considered. In Paths 1 and 2 the C—H bond of the terminal carbon atom is added giving rise to two products. If the addition proceeds in the manner of metal hydrides, the product is 2-hexene (Path 1) for acidic-type addition (Markovnikov rule), the product is 4-methyl-2-pentene (Path 2). In Paths 3 and 4, the C—H bond of the middle carbon atom is added," giving rise to 2-methyl-l-pentene (hydridic-type addition) and to 2,3-dimethyl-l-butene (acidic-... 

Similar unsatisfactory results, usually with even lower inductions are obtained with other terminal aliphatic alkenes such as 1-pentene, 2-methy]-l -butene, 3-methyl-l -butene, 2,3-dimethyl-l-butene, 3,3-dimethyl-l-butene, 2,3,3-trimethyl-l-butene, 2-ethyl-l-hexene, I-hex-ene and 1-octene (Table 1). 

When the enantiomerically enriched alkene (5)-3-methyl-l-hexene is employed, 3-ethyl-l-hexanal is formed with 70% retention of configuration together with 4-methyl-l-heptanal and 2,3-dimethyl-l-hexanal, in spite of the fact that the precursor of this product should be achiral 2-ethyl-l-pentene generated through isomerization of (5)-3-methyl-l-hexene. In order to accommodate this result, a 1,2-hydrogen shift mechanism has been proposed that does not include a true cr carbon-Co bond and is faster than the dissociation of olefin from the olefin-Co complex, which appears to be generally accepted. 

A square-planar nickel hydride complex is suggested as the catalytic species [589]. In the first step, the nickel hydride catalyst adds across the double bond of propylene to give two intermediates, namely, a propyl nickel and isopropyl nickel complex. Both of these intermediates can react further with propylene by insertion of the double bond into the nickel-carbon bond, resulting in formation of four more intermediates. ( -Elimination of nickel hydride from these intermediates produces the possible products of propylene dimerization, namely, 4-methyl-1-pen-tene, cis- and trans-4-methyl-2-pentene, 2,3-dimethyl-l-butene, n-hexene, 2-hexene, and 2-methyl-l-pentene. Terminal unbranched olefins are rapidly isomerized under the influence of catalyst by a process of repeated nickel hydride addition and elimination to the internal olefins. Therefore, under ordinary reaction conditions the yield of 4-methyl-l-pentene is low. 

Ni(acac)2-(C2H5)3Al2Cl3-PCy3 methylpentenes (36.9%), 2,3-dimethyl-l-pentene (60%), 2,3-dimethyl-2-butene (1.2%), 4-hexene (1.0%) 709... 

C2H5A1C1-H20) 2-pentene (13.2%), trans-4-methyl-2-pentene (15.2%), 2,3-dimethyl-l-pentene (43.1%), 2-methyl-l-pentene (13.3%), n-hexenes (3.3%) ... 

Ni(CH2=CHCN)2-R6-,Al3CU- PR3 4-methyl- 1-pentene, 2-methyl-2-pentene, 2- methyl-l-pentene, 2-hexene, 3- hexene, 2,3-dimethyl-l-butene, 2,3-dimethyl-2-butene 752, 753... 

It is evident from Table 11 that the rate of addition of the triplet bis(methoxy-carbonyl) carbene is somewhat slower than that of the singlet. Another important general rule may also be deduced from Table 11 the triplet carbene adds to dienes about 3—4 times faster than to olefins the reactivity ratio of 2,3-dimethyl-butadiene-1,3/pentene-l is 9.6 for triplet and 2.8 for the singlet. This ratio may be compared with that for diphenylcarbene (1,3-butadiene/hexene-l), which is > 100. 

Growe and co-workers independently reported a procedure for the cyclization/hydrosilylation of enones and enals similar to that reported by Buchwald." As an example, reaction of a 1 1 mixture of 3,3-dimethyl-5-hexenal and triethoxysilane catalyzed by Gp2Ti(PMe3)2 (20 mol%) in pentane at room temperature for 3 h gave m-l,l,3-trimethyl-4-triethoxysilyloxycyclopentane in 88% yield as a single diastereomer (Equation (38)). 

The metabolism of oleftnic or acetylenic substances to electrophilic metabolites is greatly reduced when the oleftnic or acetylenic moieties are not terminal, or are terminal but contain alkyl substituents on the allylic and propargylic positions. 1-Heptene, for example, is bioactivated to electrophilic metabolites whereas 3-hexene, 2-methyl-l-hepteneand3,3-dimethyl-l-hexenearenot [36,37]. Similarly, 1-decyneismetabolizedto electrophilic metabolites whereas 3- and 5-decynes are essentially not [36, 37]. 

Butene 1-Bromo-3,3-dimethyl-l-fluoro- E10b2. 101 (Educt) 1-Hexene 1-Bromo-2-fluoro- ElOa, 239 (In + EBr) ElOb,. 375 (In I HE/N-Br — amine)... 

Hexene 95.0 4-Methyl-2-pentene 127.5 3.3- Dimethyl-l-butene 2.3- Dimethyl- 1-butene 129.0 138.0... 

It was now important to examine the question of a possible stereochemical influence on diperoxide formation. We have approached this problem initially by ozonizing olefins of type 2. When either cis- or trans-3,4-dimethyl-3-hexene are ozonized, presumably a single stereoisomeric pair of diperoxides can be formed. In fact, this case is complicated by the possibility of two trans-diperoxide conformers being produced. The cis-diperoxide conformers are identical. Ozonolysis of cis-3,4-dimethyl-3-hexene, 8, for example, could give the diperoxides, cis-l,3-dimethyl-l,3-diethyl-2,3,5,6-tetraoxacyclohexane, 11a, and rans-l,3-dimethyl-l,3-di-ethyl-2,3,5,6-tetraoxacyclohexane, lib, with the latter capable of existing as conformers lib and lib with trans-diaxial methyl and trans-diaxial ethyl substituents, respectively. 

A) Cyclohexane B) 2-hexene C) 3-methyl-l-pentene D) 1,3-hexadiene E) 3,3-dimethyl-l-butene... 

Fig. 1. Correlation of the rate data by means of the reduced Taft-Pavelich equation 1, 1-hexene 2, l-hcptene 3, 1-octene 4, 3,3-dimethyl-l-butene 5, 4-methyl-1-pentene 6, 4,4-dimethyl-1-pentene 7, 2,3-dimethyl-1-butene 8, tran.v-3-heptene 9, zrani -4-nonene 10, (rani-4-methyl-2-pentene 11, 2-methyl-1-hexene 12, trflni-2-hexene 13, 2-methyl-2-hexene 14, 2,4-dimethyl-2-pentene 15, 2,3-dimethyl-2-butene.

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