CYCLOHEXANE, 5-METHYL-1-METHYLENE-2-

A reaction that introduces a second chirality center into a starting material that already has one need not produce equal quantities of two possible diastereomers Con sider catalytic hydrogenation of 2 methyl(methylene)cyclohexane As you might expect both CIS and trans 1 2 dimethylcyclohexane are formed... 

The relative amounts of the two products however are not equal more as 1 2 dimethyl cyclohexane is formed than trans The reason for this is that it is the less hindered face of the double bond that approaches the catalyst surface and is the face to which hydro gen IS transferred Hydrogenation of 2 methyl(methylene)cyclohexane occurs preferen tially at the side of the double bond opposite that of the methyl group and leads to a faster rate of formation of the cis stereoisomer of the product... 

The double bond m 2 methyl(methylene)cyclohexane is prochiral The two faces however are not enantiotopic as they were for the alkenes we discussed m Section 7 9 In those earlier examples when addition to the double bond created a new chirality cen ter attack at one face gave one enantiomer attack at the other gave the other enantiomer In the case of 2 methyl(methylene)cyclohexane which already has one chirality center attack at opposite faces of the double bond gives two products that are diastereomers of each other Prochiral faces of this type are called diastereotopic... 

The hydrogenation of 2 methyl(methylene)cyclohexane is an example of a stereo selective reaction meaning one m which stereoisomeric products are formed m unequal amounts from a single starting material (Section 5 11)... 

Could the fact that hydrogenation of 2-methyl(methylene)cyclohexane gives more c/s-1,2-dimethylcyclohexane than trans- be explained on the basis of the relative stabilities of the two stereoisomeric products ... 

Cyclohexanemethanol, a,a,4-trimethyl-, acetate. See Dihydroterpinyl acetate Cyclohexane, 1,1 -methlenebis (4-isocyanato-). See Methylene bis (4-cyclohexylisocyanate) Cyclohexane, methyl-. See Methyl cyclohexane Cyclohexane, (1-methylethyl)-. See Isopropylcyclohexane Cyclohexane, (1-methylpropyl)-. Sees-Butylcyclohexane... 

Methylbenzophenone o-Methyl benzoyl benzoate Methyl bromide 3-Methyl-2-butanol Methyl cyanoacetate Methyl cyclohexane Methylcyclopentane Methylene iodide Methyl 2-furoate Methyl heptenone... 

Based on the percent composition of the products for the hydrogenation of 2-methyl-methylene-cyclohexane, predict the product(s) of the hydrogenation of 2-r rr-butyhnethylenecyclohexane. 

J361 to over 5700, mw — 38000—600000, colorl, amorph or cryst, mp 240—250°, d (amorph) 1.04—1.065g/cc RI 1.59—1.60. Sol in CCI4, et benz, tol, et acet, benz, methyl et ketone, chlf, tetrahydrofuran, methyl isobutyl ketone, methylene chloride, o-dichlorobenz, py and cyclohexane. Styrene polymer can be prepd in many ways. The simplest procedure is that of heating the pure monomer. The general reaction can be represented as ... 

Scheme 5.1 illustrates some hydrogenations in which the syn addition from the less hindered side is observed. Some exceptions are also included. Entry 1 shows the hydrogenation of an exocyclic methylene group. This reaction was studied at various H2 pressures and over both Pt and Pd catalysts. 4-Methyl- and 4-r-butylmethylene cyclohexane also give mainly the cis product.3 These results are consistent with a favored (2.3 1) equatorial delivery of hydrogen. 

Methyl-2-methoxypropane, b572 7 -Methyl-3 -methylene-1,6-octadiene, m467 1 -Methyl-4-( 1 -methylethenyl)cyclohexane, d736... 

Structurally novel /3-lactams were obtained using enantiopure 4-oxoazetidine-2-carbaldehydes and methylene cyclohexane and a-methyl styrene (Equation (4)).7 Boron trifluoride diethyletherate and tin(iv) chloride produced the products in the highest yields, and all ene products possessed yy/z-stereochemistry. 

Chiral bisoxazolines (box) ligands have been attached to a polyethylene glycol (PEG) matrix 25.24 The supported ligands were tested on a variety of reactions for their enantioselectivity. The carbonyl-ene reaction between a-methyl styrene or methylene cyclohexane (26, Equation (15)) and ethylglyoxalate 12 afforded the corresponding ene adduct 27 in 96% and 91% yield and 95% and 85% ee, respectively. 

An enantioselective imino-ene reaction was developed by Lectka to provide ct-amino acid derivatives.27 Aryl alkenes (cr-methyl styrene, tetralene), aliphatic alkenes (methylene cyclohexane), and heteroatom-containing enes, all gave high yields and high ee s of the homoallylic amides (Equation (17)). The mechanism of this reaction has been proposed to proceed through a concerted pathway. This mechanism is evidenced by a large kinetic isotope effect observed in the transfer of H(D). 

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