Dimethyl- iodomethane

Catalytic hydrogenation of dimethyl 3-methyl-3//-3-benzazepine-2,4-dicarboxylate (10) to the 1,2,4,5-tetrahydro derivative with hydrogen and a palladium-barium sulfate catalyst, followed by treatment of the reaction mixture with iodomethane in refluxing methanol, yields a mixture of the 2,4-dicarboxylic acid 11 and the methiodide salt 12.24... 

Numerous procedures for the preparation of butenolides have been developed. Font and coworkers (234-236) prepared the 5-O-substituted derivatives 223a-c of D-ribono-1,4-lactone. The cw-glycol system of223a reacted with ATjV-dimethylformamide dimethyl acetal and then with iodomethane to give the trimethylammonium methylidene intermediate 224. Pyrolysis of 224 gave the butenolide 225. 

The ambident nature of the anion (121) affords an explanation for the formation of both OO-diethyl 7V-methylphosphoramidate and OO-diethyl AW-dimethyl-phosphoramidothionate when diethyl iV-methylphosphoramidothionate anion is treated with iodomethane, followed by aqueous work-up.91... 

Metallation of 63 with butyllithium preferably proceeds in positions 1 and 6 subsequent reaction with iodomethane or carbon dioxide led to the corresponding dimethyl derivative 66 or esters 67-69. An unusual addition of butyllithium to the central double bond of 63 was also observed to a small extent producing 70 (Scheme 3) <200(Ki CC58>. 

Reaction of the quaternized salts of 4-ethoxycarbonyl-3,5-dimethyl-f-phenylpyttolo(furo or thieno)[2,3-c]pyrazole 34 with the iodomethane quaternary salts of pyridine, quinoline, and isoquinoline in ethanol with catalytic piperidine gave 3-[4(f)]-monomethine cyanine dyes (e.g., 35). Additionally, 3-[2(4)]-trimethine cyanine dyes and 4-[2(4)]-di-3[2(4)]-tri-mixed methine cyanine dyes (e.g., 36 and 37, respectively) were similarly prepared from the intermediates derived by reaction of 34 with triethyl orthoformate in the presence of piperidine (Scheme 8) <2002CCS106f>. 

The enantiomerically pure l-[(benzyl(dimethyl)silyl)methyl]pyrrolidine, obtained from ben-zyl(chloro)(dimethyl)silane and (5,)-2-(methoxymethyl)pyrrolidine , afforded after deprotonation and subsequent alkylation the diastereomerically pure (by NMR spectroscopy) (a-alkylben-zyl)silanes2. To obtain this high degree of diastereoselectivity, the alkylation had to be performed in the weakly complexing solvent diethyl ether. In THF a diastereomeric ratio of only 3 1 was found with iodomethane as alkylating agent. 

The dependency of asymmetric induction on the nature of the electrophile has been demonstrated in the synthesis of (7 )-2-methylcyclohexanone. Thus, the enantiomeric excess dropped from 99% to 67% wheniodomethane was used instead of dimethyl sulfate as alkylating agent6 and the use of methyl 4-methylbenzenesulfonate as electrophile resulted in a dramatic increase to >98% ee from that of 61 -75% ee when iodomethane was used9. 

These results are supported by those from the reaction of (Z)-l-(ethylsulfmyl)-2-(ethyl-thio)ethene with iodomethane or dimethyl disulfide. 

The enolates of both cyclobutanones and acylcyclobutanes are readily formed and react smoothly with alkyl halides152,159 171,341 or carbonyl groups.92,103,, 04 172 175 However, caution is required to avoid O-alkylation in the former case. For example, dimethylation of 2,2,3,3-tetramethylcyclobutanone with potassium hydride and iodomethane gave 2,2,3,3.4,4-hexamethylcyclobutanone (2) together with l-methoxy-2,3,3,4,4-pentamethylcyclobutene (3) in a 93 6 ratio.159... 

Nucleophiles attack the imide sulfur atom of trithiadiazepines. Trithiadiazepine (29, R = H) is converted by potassium t-butoxide and iodomethane into 3,4-dimethylthio-l,2,5-thiadiazole (30) by a rearrangement in which two of the ring sulfur atoms have become exocyclic with triphenylphosphine (29, R = C02Me) gives dimethyl l,2,5-thiadiazole-3,4-dicarboxylate (28) (87JCS(Pl)2i7). 

In an interesting reaction reported by Salerni et al.,13i the disulfide 61 was cleaved by iodomethane at the -CH2-S- bonds with concomitant cyclization releasing dimethyl disulfide, forming the 2-iminothiazolidine 62. 

The chemistry of benzo[Z>]furan-2(3//)-one (395) which exists in the keto form, is that expected of the lactone of 2-hydroxyphenylacetic acid. Grignard reagents bring about the expected ring opening. Condensations may be effected at the 3-position, especially with aromatic aldehydes. Methylation with iodomethane and potassium carbonate in DMF furnishes the 3-methyl and the 3,3-dimethyl compound. Methylation, with diazomethane,... 

Af-Alkylation of polyheteroatom six-membered rings is readily achieved. For example, the oxadiazine (72) gives the 4-methyl derivative <75CB19ll), and the oxadiazinedione (73) gives a mixture of mono- and dimethyl derivatives (79JHC161) on treatment with iodomethane. 

The alkylation of the 1,2,6-thiadiazine (76) has been studied in detail (82H(l7)40l) because of its importance as an isostere of 6-methyluracil. Dimethyl sulfate in the presence of sodium hydroxide as base gives the 2-monomethyl derivative exclusively. Other reagents such as diazomethane and iodomethane give the 2,6-dimethyl derivative as the major product although substantial amounts of O-methylation and C-methylation at C-4 also occur, indicating that in systems where there are several possible sites for alkylation, the results are very much dependent on the reaction conditions. 

Diazomethane Dimethyl sulphate Epichlorhydrin Iodomethane (methyl iodide)... 

Another methylation method makes use of a reaction with iodomethane and a catalyst [478], as follows. About 30 mg of an oil dispersion of sodium hydride was washed three times with anhydrous diethyl ether, dried under a mild stream of nitrogen and suspended in 1 ml of freshly distilled dimethyl sulphoxide. A 200-jul portion of this suspension was added to ca. 1 /amol of phenylurea dissolved in 100 pi of pure dimethyl sulphoxide followed immediately by 50 pi of iodomethane. Reaction was allowed to proceed for 5—10 min with continuous stirring. Then 1 ml of water was carefully added and the mixture was extracted with three 1-ml portions of diethyl ether or light petroleum. The extracts were dried with anhydrous sodium sulphate, filtered and evaporated to dryness under a stream of nitrogen. Silicone stationary phases [OV-225 at 108°C or a mixture of DC-200 and QF-1 (1 3) at 170°C] were used. 

Methyl ethers are usually prepared by some variant of the Williamson ether synthesis in which an alcohol reacts with either iodomethane, dimethyl sulfate, or methyl triflate (HAZARD) in the presence of a suitable base. A word of caution dimethyl sulfate and methyl triflate, tike all powerful alkylating agents, are potentially carcinogenic and therefore should only be handled in a well-ventilated fume hood. For the 0-methylation of phenols (pKa 10) a comparatively weak base such as potassium carbonate in conjunction with dimethyl sulfate is sufficient,193 whereas simple aliphatic alcohols require stronger bases such as sodium hydride [Scheme 4.111]22 or lithium hexamethyldisilazide [Scheme 4.112].203 The latter transformation is notable for the fact that 0-methyiation was accomplished without competing elimination. 

Methylation of polysaccharides is now speedily and efficiently achieved by treating them in dimethyl sulfoxide with sodium methyl-sulfinylmethanide and iodomethane.1783 It is well known that strong bases, and, in particular, the base mentioned, cause a /3-elimination... 

The Af,lV -dimethyl derivative 4 is obtained in three steps by formation of the corresponding imidazolidine with acetone, alkylation with iodomethane, and hydrolysis (eq 3). 

Quinazoline-2,4(l//,3//)-dithione furnishes with iodomethane in aqueous sodium hydroxide 2,4-bis(methylsulfanyl)quinazoline," whereas with an excess of boron trifluoride-dimethyl ether complex in hot nitrobenzene, 2-(methylsulfanyl)quinazoline-4(3i/)-thione is obtained. ... 

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