ACID CHLORIDES FROM a-KETO ACIDS

Acetylenes, homologation to allenes, 63, 203 Acetylenes, in peptide synthesis, 63, 175 a,B-ACETYLENIC KETONES, ASYMETRIC REDUCTION OF, 63, 57 ACID CHLORIDES FROM a-KETO ACIDS, 61, 1 Acrolein [107-02-8], 62, 140... 

ACID CHLORIDES FROM a-KETO ACIDS WITH a,a-DICHLOROMETHYL METHYL ETHER PYRUVOYL CHLORIDE... 

Cobaltous chloride/potassium cyanide Homogeneous hydrogenation with cobalt complexes a-Amino- from a-keto-carboxylic acids... 

Alternate Preparations Of a-Keto Esters From Acid Chlorides," Katritzky. A.R. Wang, Z. Wells, A.P. Org. Prep. Proceed. Int., 1995, 21, 457... 

Pyrazolinones and isoxazolinones are prepared from (3-keto esters and hydrazine or hydroxylamine by reactions such as (34 — 35) similar to those in (i) above. Diketene behaves as a masked (3-keto ester. Acetylenecarboxylic esters can be used in place of (3-keto esters to give pyrazolinones such as (36) and (37) and the corresponding isoxazolinones. (3-Chloro-a,(3-unsaturated acid chlorides react similarly (cf. 38 — 39). 

Dinitrophenylhydrazones (DNPHs) were applied to the GC analysis of keto acids. As with carbonyl compounds, they are prepared by reaction with 2,4-dinitrophenylhydrazine and are also used mainly for the preliminary isolation of keto acids. They can be isolated from a dilute aqueous sample by adsorption on activated carbon and selective desorption [178] hydrazones of aldehydes with a methyl formate-dichloromethane mixture and hydrazones of keto acids with a pyridine-water azeotropic mixture. Hydrazones of acids are released from their pyridine salts with methanol containing hydrogen chloride. After... 

Most of the conventional reagents for the synthesis of acid chlorides from carboxylic acids are unsatisfactory for the preparation of a-keto acid chlorides. For example, the reaction of pyruvic acid with phosphorus halides does not give pyruvoyl chloride7 whereas the use of phosgene8 or oxalyl chloride9,10 affords ether solutions of the acid chloride in low yield. Recently a useful preparation of pyruvoyl chloride from trimeth-ylsilyl pyruvate and oxalyl chloride has been described.11... 

The hydroxy part of a hydroxy acid can also be activated for macrolactonization. Vedejs et al. [60] applied such a strategy to the synthesis of the macrocychc pyrrolizidine alkaloid monocrotaline 108). Thus, the seco acid derivative 106 was first mesylated with MsCl/EtjN in dichloromethane, and the crude product was added over 3 h to an excess of tetrabutylammonium fluoride trihydrate in acetonitrile at 34 °C to effect ring carboxy deprotection and ring closure to give 107 in 71% yield (Scheme 36). It has been noted that the active intermediate of this kind of lactonization may be an allylic chloride rather than a mesylate [61a], In addition, an intramolecular nucleophilic displacement process of chloride from an a-chloro ketone moiety by a remote carboxylate has been recently reported as an efficient approach to macrocychc keto lactones [61 bj. 

Although the selfcondensation of amide chlorides proceeds well to give amide chlorides derived from 3-keto acids (56 equation 35) this reaction has only been used to synthesize 3-keto acid amides, which result after hydrolysis of the condensation products (56), and not to prepare the salts (56) in the pure state. The condensation reaction of aromatic aldehydes with the //A -dimethylacetamide-POCb adduct... 

The synthon of the a-acrylate anion is available from a secondary a-keto carboxamide by the Shapiro reaction. The secondary a-ketoamide trisylhydrazones ate ptepar in a one-pot synthesis by reaction of the isocyanides with acid chloride, water and trisylhydrazine in sequence. In DME solvent, the hydra-zone (103) is smoothly metallated with BuLi to give Ae trianion (KH). Allylation of the trianion (104) gives the hydrazone (105). Alternatively, warming (104) up to room temperature yields the dianion (106) which can be intercepted with several electrophiles (Scheme 23). The adduct (107) is readily transformed into the rran -iodo lactone (108) stereospecifically (equation 56). This chemistry also has been applied to a new synthesis of -lactams (Scheme 24). ... 

---