From Diazo-keto-amides

From Diazo-keto-amides. A classical synthesis of 1,2,3-thiadiazoIes (3) involves the cyclization of a-diazo-/3-keto-amides (2) with hydrogen sulphide and catalytic amounts of ammonia. Under similar conditions, diazo-compounds of structure [4 R = Me or Et, RR = (CHj)6l gave the hydrazones (5) rather than the desired 1,2,3-thiadiazoles (3). ... 

Aldehydes react with the lithio-derivatives of a-diazo-esters to give /3-hydr-oxy>a-diazo-esters, which in turn undergo rhodium(ii)-catalysed decomposition to give /3-keto-esters./3-Keto-amides are obtained in moderate to high yield from the acylation of amide enolates with mixed anhydrides. In a general reaction, orthoformates react with acidic methines to give /3-keto-aldehydes, isolated as their dialkyl acetals [equation (16)]. ... 

Diazocarbonyl compounds can be prepared on insoluble supports by diazo group transfer with sulfonyl azides or by diazotization of primary amines. Diazo group transfer from sulfonyl azides to 1,3-dicarbonyl compounds proceeds on cross-linked polystyrene as smoothly as in solution (Table 10.19). When 3-keto esters or amides are... 

Some synthetic approaches to pyrazines relied on metal-assisted reactions. A synthesis of 6-substituted 5H-pyrrolol2,3-bJpyrazines via Pd-catalyzed heteroannulation from W-(3-chloropyrazin-2-yl)methanesulfonamide and alkynes was developed <04TL8087>, and 3- and 5-substituted 2(l//)-pyrazinones were prepared by Suzuki and Heck reactions using 3,5-dichloro-2(l//)-pyrazinones <04TL1885>. An improved synthesis of 6-substituted-5//-pyrrolo 2,3-iiJ-pyrazines via microwave-assisted Pd-catalyzed heteroannulation was developed <04TL8631>, and the reaction of a-diazo-P-keto esters with Boc amino acid amides in the presence of a Rh catalyst gave, after air oxidation, pyrazin-6-ones 111, which were then converted into tetrasubstituted pyrazines 112 <04OL4627>. 

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