Methyl iodide, quaternization reagent

The insight that zinc ester enolates can be prepared prior to the addition of the electrophile has largely expanded the scope of the Reformatsky reaction.1-3 Substrates such as azomethines that quaternize in the presence of a-halo-esters do react without incident under these two-step conditions.23 The same holds true for acyl halides which readily decompose on exposure to zinc dust, but react properly with preformed zinc ester enolates in the presence of catalytic amounts of Pd(0) complexes.24 Alkylations of Reformatsky reagents are usually difficult to achieve and proceed only with the most reactive agents such as methyl iodide or benzyl halides.25 However, zinc ester enolates can be cross-coupled with aryl- and alkenyl halides or -triflates, respectively, in the presence of transition metal catalysts in a Negishi-type reaction.26 Table 14.2 compiles a few selected examples of Reformatsky reactions with electrophiles other than aldehydes or ketones.27... 

Carbonyldiimidazole 820 can be used to convert alcohols into alkyl halides by a one-step reaction using an excess of such reactive halides as allyl bromide or methyl iodide, and 820 can be made even more reactive by quaternization. The disadvantages of 820 are its cost and the fact that phosgene must be used in its preparation. An alternative is 1,1-oxalyldiimidazole 821 (made from 1-trimethylsilylimidazole and oxalyl chloride). Transacylation reactions occur very readily with this reagent (Scheme 176). 

Methyl acrylates." The reagent is converted by LDA into the stable ester enolate a, which is alkylated by primary alkyl iodides and allylic bromides in the presence of HMPT to give the useful Mannich bases 2. These products can be converted into methyl acrylates (4) by quaternization (quantitative) followed by treatment with diazabicyclo[4.3.0]nonene-5 (DBN) in refluxing benzene. 

Quaternization of amines. Amines (primary, secondary, and tertiary) are efficiently quaternized by methyl iodide and potassium bicarbonate in methanol at 20°. The reagent does not attack hydroxyl or phenolic groups, amides, or amino groups protected as the BOC or CBZ derivatives. ... 

Chemical Properties.—Alkylation. 3-Alkyl-2-thiazolinium salts are readily accessible by direct quaternization of the appropriate 2-thiazolines. 4-Methoxycarbonyl-2-methyl-2-thiazoline, obtainable from L-cysteine methyl ester, is rapidly A-alkylated by methyl iodide and other reagents (Scheme 11). 

Oxazines. The synthetic utility of dihydro-1,3-oxazines ° has been considerably extended by Meyers. The reactivity of the double bond in dihydro-oxazines is enhanced on quaternization with methyl iodide the resulting salt readily adds a range of organometallic reagents, affording the versatile ketone synthesis summarized in Scheme 62. 

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