Methyl position

New copolymers based on a copolymerization of isobutylene and p-methyl-styrene with improved heat resistance have been reported [64]. Once copolymerization was accomplished, the polymer was selectively brominated in the p-methyl position to yield a terpolymer called EXXPO. In contrast to butyl and halobutyl, the new terpolymer has no unsaturation in the backbone and therefore shows enhanced thermal stability and resistance to oxidation. Useful solvent-based adhesives can be formulated using the new terpolymer in combination with block copolymers [65]. The hydrocarbon nature of the new terpolymer results in excellent compatibility with hydrocarbon resins and oils. 

Highly c/s-selectivity and low molecular weight distribution polymerization of l -butadiene with cobalt(II) pyridyl bis(imine) complexes in the presence of ethylaluminum sesquischloride effect of methyl position in the ligand... 

Other phosphorous compounds, as shown in Table 8, were resolved by the same procedure. The three isomeric phosphinates 27b-d containing a methyl group attached to the aryl substituent could also be resolved, irrespective of the methyl position. From the related phosphine oxides 28a d, however, only those with R=H (28a) and R=m-CH (28c) could be well resolved no satisfactory resolution could be obtained for the other isomers of 28. The efficiency of the optical resolution of alkylaryl-substituted sulfoxides and selenoxides was found to depend similarly on the type of substitution on the aryl ring. 

The complex TpPtMeH2 was synthesized by reacting TpPtMe(CO) with water (66). While it is stable towards reductive elimination of methane at 55 °C, deuterium incorporation from methanol-c/4 solvent occurs rapidly into the hydride positions and subsequently, more slowly, into the methyl position (Scheme 15). The scrambling into the methyl position has been attributed to reversible formation of a methane complex which does not lose methane under the reaction conditions (75,76). Similar scrambling reactions have been observed for other metal alkyl hydrides at temperatures below those where alkane reductive elimination becomes dominant (77-84). This includes examples of scrambling without methane loss at elevated temperature (78). 

Hirst and Woolvin169 preferentially methylated positions 3, 4 and 6 by the use of glucal, an unsaturated sugar derivative having a 1,2-olefinic bond, introduced by the reduction of triacetyl-a-D-glucopyranosyl bromide with zinc dust and acetic acid. By the action of an ethereal solution of perbenzoic acid on an aqueous solution of 3,4,6-trimethyl-glucal a sirupy product was obtained. This was shown to contain... 

Methylated Position (Compound) A Er (kcal/mol) Gas Phase (Aqueous Phase) q < CH3 (A qCH/ GIAO-NMR SI3C (A6I3C) (ppm/ Biological Activityd... 

In general, the product ratio of a mixed aldol condensation will depend upon the individual reaction rates. Most ketones show a pattern similar to butanone in reactions with aromatic aldehydes. Base catalysis favors reaction at a methyl position over a methylene group, whereas acid catalysis gives the opposite preference. 

Reactions occnr smoothly at room temperature, affording the enolate prodncts 30-32 as isolated crystalhne solids (in 35-78% yields). In these reactions, 2,4,6-trimethylaceto-phenone is selectively deprotonated at the methyl position and no nucleophilic side-reactions take place. 

It must be concluded, however, that the stages of biosynthesis at which ring contraction and the loss of the C-12 acetate carboxyl occur are still unknown. It is open to conjecture whether introduction of the remaining five methionine derived methyl groups occurs at the isobacteriochlorin level or after extrusion of the C-20 meso- carbon. It has been shown that the CD3 groups of [CD3]methionine are transferred to all seven methylated positions without loss of deuterium. 

Coates and co-workers have also investigated a wide variety of compounds of the type (RBeX) , where R=CH3 or C2H5 and X=NMe2, OMe, SeEt, SeO, SC2H4NMe2, etc., and n = 2 or 3 (9, 10, 23-25). In a number of the trimeric derivatives, they have postulated that the ring structure can be present in two conformations with rapid conversion from one to the other at room temperature. In some instances, these conformations may be slowed to give resolvable methyl resonances corresponding to the nonequivalent methyl positions. No quantitative data have been presented on these systems. 

Methoxyquinoline is regioselectively oxidized at the methyl group by a chelate-directed palladium-catalyzed C-H bond activation <2004JA2300>. 8-Methylquinoline is selectively oxidized at the methyl position on treatment with palladium(ll) acetate followed by the oxidant phenyliodinium diacetate in acetic acid. The reaction proceeds via formation of a palladacycle (Scheme 4). Performing the reaction in methanol leads to isolation of 8-(methoxy-methyl)quinoline in 77% yield. 

Alkyl groups at the 2- and 4-positions of the pyridine ring are electron deficient due to loss of electron density to the ring nitrogen by resonance and induction. A consequence of this effect is the relative ease of deprotonation at the 2- and 4-methyl position to give resonance-stabilized anions (Equations 26 and 27). 

It is possible to halogenate selectively at the methyl position of alkylpyridines to give halogenoalkylpyridines. Low to moderate yields of fluoromethylpyridines are obtained on fluorination of 2- and 4-methyl pyridines with (V-fluoro-bis[(trifluoromethyl)sulfonyl]imide 52 in the presence of sodium carbonate in dichloromethane <1996T15>. 2-Methylpyridine is fluorinated in 20% yield and 4-methylpyridine in 72% yield under these conditions. Reagent 52 also effects the selective fluorination of 2,4,6-collidine to give the 2-fluoromethylated product in moderate yield (Equation 35). 

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