Diazomethane, with acyl halides

The reaction between acyl halides and diazomethane is of wide scope and is the best way to prepare diazo ketones. Diazomethane must be present in excess or the HX produced will react with the diazo ketone (10-74). This reaction is the first step of the Amdt-Eistert synthesis (18-8). Diazo ketones can also be prepared directly from a carboxylic acid and diazomethane or diazoethane in the presence of dicyclohexyl-carbodiimide. ... 

Esters of a-hydroxymethyl ketones are formed by heating diazoketones with organic acids. The crude diazoketones prepared from acyl halides and diazomethane may be used. The over-all yields of acetoxy ketones, ArCOCHjO,CCHj, from benzoyl and /3-naphthoyl chlorides are 55% and 72%, respectively. ... 

Methylation of 1-hydroxyindoles can be achieved readily by the reaction with diazomethane, Mel, orMc2S04 in the presence of an appropriate base, as described in previous reviews (79MI1, 90AHC105, 91YGK205, 99H1157). Alkylation and acylation also work well with alkyl halides, acyl halides, acid anhydrides, and acids in the presence of acid activators such as DCC and so on. 

The reaction is of wide scope (R = alkyl, aryl) however the substrate molecule should not contain other functional groups that can react with diazomethane. With unsaturated acyl halides the yield can be poor, but may be improved by modified reaction conditions. ... 

The most frequently used ylides for carbene-complex generation are acceptor-substituted diazomethanes. As already mentioned in Section 3.1.3.1, non-acceptor-substituted diazoalkanes are strong C-nucleophiles, easy to convert into carbene complexes with a broad variety of transition metal complexes. Acceptor-substituted diazomethanes are, however, less nucleophilic (and more stable) than non-acceptor-substituted diazoalkanes, and require catalysts of higher electrophilicity to be efficiently decomposed. Not surprisingly, the very stable bis-acceptor-substituted diazomethanes can be converted into carbene complexes only with strongly electrophilic catalysts. This order of reactivity towards electrophilic transition metal complexes correlates with the reactivity of diazoalkanes towards other electrophiles, such as Brpnsted acids or acyl halides. 

Because many more alcohols than alkyl halides are commercially available, the Mitsu-nobu reaction enables the synthesis of larger and more diverse compound arrays than alkylation with alkyl halides. A -AcyIsuIfonamides are strongly acidic and can be alkylated with diazomethane (Entry 6, Table 8.9) or trimethylsilyldiazomethane [137]. Resin-bound sulfonamides have been N-acylated by treatment with acyl halides, and N-carbamoylated by treatment with isocyanates [138]. 

Diazocarbonyl compounds can also be prepared by C-acylation of diazoalkanes with polystyrene-bound acyl halides (Entry 6, Table 10.19). As an alternative to diazomethane, the more stable a-(trimethylsilyl)diazomethane may be used, which is sufficiently nucleophilic to react with acyl halides. On heating, the resulting a-(trimethyl-silyl)diazo ketones undergo Wolff rearrangement to yield ketenes, and have also been used as starting materials for the preparation of oxazoles [368]. 

In an earlier chapter, we saw how to reduce the carbon chain by one methylene unit using the Hunsdiecker reaction. The opposite of this, namely the extension of the carbon chain by one unit, may be achieved with the Amdt-Eistert synthesis. In the first step, an acyl halide is treated with diazomethane to form the a-diazo ketone. This is then treated with water and silver oxide. The resultant product is the free acid. If an alcohol is used instead of water, then the related ester is formed. Suggest what is the pathway for this reaction. 

A facile assembly of 2,4-orthogonally-functionalised oxazoles as useful bidirectional linchpins was achieved by treatment with diazomethane of acyl isocyanates, generated in situ from acyl halides 132 oxazolones 133 were converted to the oxazole triflates 134, useful intermediates for further synthetic elaborations as highlighted by the synthesis of 135 via Wittig and Stille reactions <01SL1739>. This linchpin tactic was used in the stereocontrol led total synthesis of the potent cytostatic agent (+)-phorboxazole A <01JA10942>. 

Triazole undergoes halogenation, and bromination of the triazole provides the 4,5-dibromo derivative. The 4,5-dibromotriazole was prepared by bromination of triazole with NBS. Triazoles are readily alkylated on nitrogen by alkylhalides, dimethylsulfate, diazomethane, and conjugate addition. In addition, triazoles are acylated by acyl halides and anhydrides and the alkylations are not regioselective. ... 

In the Barbier-Wieland degradation, the alpha-methylene group in an aliphatic carboxylic acid is removed in a sequence of reaction steps, effectively a chainshortening. The inverse procedure is the Amdt-Eistert synthesis, where an acid is converted into acyl halide and reacts with diazomethane to give the highest homolog. 

A much more general method for acyl silane synthesis involving silyl diazo intermediates is illustrated in Scheme 1688. The lithiated derivative of trimethylsilyl diazomethane reacts smoothly with alkyl halides in THF solution to give a-trimethylsilyl diazoalkanes in good yields. Oxidative cleavage of the diazo moiety is effected using 3-chloroperbenzoic acid in benzene solution, to give access to a wide variety of acyl silanes in yields of up to 71%. A phosphate buffer (pH 7.6) is used to prevent side reactions. Aromatic acyl silanes clearly cannot be prepared by this chemistry since an aromatic nucleophilic substitution reaction would be required. 

The free N-H group in pyrazole can be alkylated with alkylating agents such as alkyl halides, diazomethane, and dimethyl sulfate or acylated using acid chloride and acetic anhydride. 

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