Azidoformate esters

Azidoformic esters such as 342 react with Cgg in a [2-tl] addition (Scheme 4.70), if the temperature is high enough to induce the loss of nitrogen prior to addition, otherwise a [3-1-2] addition can be observed (Section 4.3.2) [172, 395, 397]. Typical conditions include heating of the mixture in solvents such as tetrachloroethane [395, 397, 398], chloronaphfhalene [397] or toluene [396] at 110-160 °C. These conditions also afford multiple addition products [172]. To avoid potential hazard during purification of the azido formiates, they were also generated in situ in one pot by the reaction of chloro-formic ester with sodium azide [396]. 

Azidoformate esters, N3CO2R, also can show the Curtius rearrangement. A low yield (ca. 10%) of a trimer of methoxyisocyanate was isolated after irradiation of methylazidoformate in aprotic media , but generally both photolysis and thermolysis lead to similar products of secondary reactions that are characteristic of the formation of nitrenes with the rearrangement product either not present or in very minor yield. In aromatic solvents insertions can lead to... 

Note that sulfonyl azides and azidoformate esters form N-allyl sulfonamides and carbamates, respectively, in the free-radical reactions (using Ph3SnCH2CH=CH2 as the allyl donor)."]... 

Aluminum chloride [7446-70-0] is a useful catalyst in the reaction of aromatic amines with ethyleneknine (76). SoHd catalysts promote the reaction of ethyleneknine with ammonia in the gas phase to give ethylenediamine (77). Not only ammonia and amines, but also hydrazine [302-01-2] (78), hydrazoic acid [7782-79-8] (79—82), alkyl azidoformates (83), and acid amides, eg, sulfonamides (84) or 2,4-dioxopyrimidines (85), have been used as ring-opening reagents for ethyleneknine with nitrogen being the nucleophilic center (1). The 2-oxopiperazine skeleton has been synthesized from a-amino acid esters and ethyleneknine (86—89). 

Tests conducted by the Eastman Kodak Company have shown that tert-butyl azidoformate [Formic acid, azido, -butyl ester], also known as iert-butoxy carbonyl azide and 1-BOC azide, is a thermally unstable, shock-sensitive compound (TNT equivalence 45%). 

The nitrene can be generated by a variety of methods, the most popular being the thermal or photolytic decomposition of azidoformates. Other methods, particularly the base-catalyzed a-elimination of arylsulfonate ion from 7V-[(arylsulfonyl)oxy]urethanes, are useful as they avoid the use of the potentially explosive azido esters. 

A solution of ethyl azidoformate (10 g, 87 mmol) in anhyd benzene (250 mL) was photolyzed at 60-70 C for 60 h, using a high-pressure Hg ultraviolet lamp, whereupon N2 was evolved and the solution became yellow. The benzene and remaining azido ester were removed under reduced pressure, and the yellow-brown oily residue distilled under high vacuum to give a yellow oil yield 8.35 g (67%) bp 46-47 C/5 x 10"3 Torr bp 130 C/0.2 Torr. 

The metalloporphyrin-catalyzed decomposition of ethyl azidoformate in the presence of an arene has been investigated but with little success in improving the yields of the 1 //-azepines.151 The nickel and copper complexes had no effect, whereas the cobalt-tetraphenylporphyrin complex accelerated the decomposition rate of the azido ester but produced more A-arylurethane rather than 1//-azepine. 

BUTYL AZIDOFORMATE (Formic add, azido-, /er/-butyl ester)... 

Azidoformic Acid Etbylester (Azidoameisen-saure-athylester, Triazoameisensaure-athyl-ester, Carbazidsaure-athylester or Stich-stoffkohlens ure-athylester in Ger),... 

Azidoformic Acid Methytester (Azidoameisen-saure-methylester, Triazoameisensaure-methylester, Carbazidsaure-methylester or Stickstoffkohleasaure-methylester in Ger), N3.CO.O.CH3 mw 101.06, N 41.58%, OB —55.4% colorless liq, bp 102—3° exploded occasionally when distilled under atm pressure. May be prepd by warming for 1 hr ethereal soln of Am azide with methyl ester of chloroformic acid, Cl.CO.O.CHg. 

Azidoformic Acid Ethylester (Azidoameisen-saure-athylester, Triazoameisensaure-athyl-ester, Carbazidsaure-athylester or Stich-stoffkohlensaure-athylester in Ger), N3COOCH2CH3 mw 114.09, N 36.88% liq, bp 11.4-15°, 34°(20.5 torr), sp gr 1.1082 at 20°, nD 1.4162 at 25°. Prepd from N-aminourethane and nitric acid (Ref 2), or by reacting NaN with chloroformic acid ethyl-ester (Ref 3)... 

The synthesis of A -Ddz-protected amino acids is generally achieved with the 2-(3,5-di-methoxyphenyl)prop-2-yl azidoformate (Ddz-Nj) which is obtained from 3,5-dimethoxy-benzoic acid by a multistep procedure. ] Protection is performed either under Schotten— Baumann conditions, or preferentially, by acylation of the amino acid benzyltrimethylam-monium salts in pyridine.b l N -Acylation of the amino acid methyl esters followed by saponification has been reported to produce the desired derivatives in higher overall yields. 

Dithiazines, urethanes, or iminocarboxylic acid esters result from the reaction of ethyl azidoformate with l,2-dithiole-3-thiones.232... 

Irradiation of acyl azides (374) results in the Curtius-type rearrangement1163 to produce the isocyanates 375 and nitrogen in a concerted fashion (no nitrene intermediates are involved) (Scheme 6.176). Esters of azidoformic acid (374, R = alkoxy) produce singlet nitrenes, which can be trapped by alkenes or inserted into a C H bond.1112,1164... 

Enamines derived from ketones undergo some of the same reactions described for enol ethers, for example with arenesulfonyloxy carbamates as in Eq. 96120 121 3" and with ethyl azidoformate as in Eq. 98.302 303 The reaction with activated azo compounds occurs readily at room temperature or below and diamination often cannot be avoided with the more electrophilic reagents (Eq. lOl).400,401 The proline-catalyzed reaction of ketones with azodicarboxylic esters, which proceeds by way of the enamines, has been mentioned above (Eq. 91). 

Ethyl azidoformate reacts with a-keto and a-ester phosphorus ylides to give 1-carboethoxy-iiic-triazoles. ... 

In contrast to other l,2-dithiole-3-thiones, which give the corresponding carboximidic esters, treatment of 4-phenyl-l,2-dithiole-3-thione with ethyl azidoformate in boiling carbon tetrachloride gives a mixture of ethyl 5-phenyl-6-thioxo-l,2,3-dithiazine-3-carboxylate (2, 57%) and ethyl (4-phenyl-5-thioxo-l,2-dithiol-3-yl)carbamate (10%).5... 

L abb6 and his collaborators have added azides to both active methylene compounds (Eq. if and acetylenes (Eq. 8) for the preparation of unusual examples of 1,2,3-triazoIes. With ethyl azidoformate (10.1-3) the initially formed 1-ester (10.1-4) rearranges on workup to the 2-substituted product... 

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