F-Butyl carbazate

A third approach to 3-amino-/3-lactams is by Curtius rearrangement of the corresponding acyl azides. These are readily prepared from r-butyl carbazides, available via photochemical ring contraction of 3-diazopyrrolidine-2,4-diones in the presence of f-butyl carbazate (c/. Section 5.09.3.3.2). Thus treatment of (201) with trifluoroacetic acid followed by diazotiz-ation gives the acyl azide (202) which, in thermolysis in benzene and subsequent interception of the resulting isocyanate with r-butanol, yields the protected 3-amino-/3-lactam (203) (73JCS(P1)2907). 

OButyl azidoformate, a useful protective group for primary and secondary amino groups,4 0 has been prepared previously from f-butyl carbazate.3 The present procedure7 is a more convenient preparative method. 1 he intermediate carbonic phosphoric anhydride reacts with nucleophiles other than the azide ion in this preparation. Reaction of this anhydride with amines yields the t-butoxycarbonyl derivatives of amines.7 Other carbonic phosphoric anhydrides have been prepared by procedures analogous to the method described here.8... 

To a solution of 17.95 gm (0.0634 mole) of f-butyl-2-(p-bromophenyl) carbazate and 4.94 gm (0.0626 mole) of dry pyridine in 300 ml of methylene chloride is added, in small portions, over a 20 min period, 11.13 gm (0.0551 mole) of N-bromosuccinimide. The red solution is allowed to stand at room temperature for 3 hr. Then the reaction mixture is washed in turn with two portions of 100 ml of water, 125 ml of 10% aqueous sodium hydroxide, and another two portions of water. The product solution is then dried with anhydrous potassium carbonate. The solvent is removed by distillation under reduced pressure, using a water bath at 50°C as the source of heat. On standing, the red liquid crystallizes to a yellow-orange solid which is dissolved in methanol, treated with charcoal, filtered, and the filtrate treated with just sufficient water to cause product precipitation yield 15.34 gm (86%), yellow-orange crystals, m.p. 66°-67°C. 

Bromophenylazo)-2/-toluene, 309 (2-BromophenyI)-iVM7-azoxy (2-hydroxy-5-methylbenzene), 358 p-Bromophenylurea, 138-139 Bromopropadiene, 17 2,3-Butadienoic add, 16 iV-l-Butenylpiperazine, 92 Butter yellow, hazard of, 291 f-Butylamine, oxidation of, 323 -Butyl azide, 269 f-Butyl-OlW-azoxymethane, 349 t-Butyl p-Bromophenylazoformate, 328 t-Butyl 2-(p-bromophenyl)carbazate, 328 H-Butyl carbamate, 238-239 t-Butyl carbamate, 241-243... 

B. i-Bulyl carbazate. In a 1-1. Erlenmeyer flask are placed 388.4 g. (2.0 moles) of phenyl f-butyl carbonate and 120.2 g. (2.4 moles) of a 64% hydrazine solution (Note 6). The mixture is swirled by hand and heated on a hot plate. When the internal temperature reaches 75-80°, it then rises rapidly and spontaneously to 104—110°, the two layers forming a dear solution. The solution is allowed to cool overnight. The mixture is then diluted with 500 ml. of ether and transferred to a separatory funnel in which it is shaken vigorously for about 10 minutes with a solution prepared from 160 g. (4.0 moles) of sodium hydroxide and 1.2 1. of water. The resulting two layers are placed in a 2-1. continuous extractor and extracted for 48 hours with ether. The ether solution is dried over magnesium sulfate, and the ether is removed by distillation from a water bath. The last portions of ether are removed with the aid of a water aspirator. The residual oil is then distilled using a Claisen flask with an air bath maintained at 115-125°. After 1 or 2 drops of fore-run the carbazate is collected at 61-65° (1.2 mm.), w24d 1.4518. The yield is 235-256 g. (89-97%) (Note 7). 

A mixture of ferf-butyl S-methyl thiolcarbonate and 64%-hydrazine refluxed 24 hrs. at 105-110° oil bath temp, with stirring ferf-butyl carbazate (startg. m. f. 517). Y 84%. L. A. Garpino, Am. Soc. 82, 2725 (1960). 

N-Bromosuccinimide added in small portions during 15-20 min. to a soln. of ferf-butyl 2-(p-bromophenyl)carbazate and pyridine in methylene dichloride, and allowed to stand 2-3 hrs. at room temp. ferf-butyl p-bromophenylazo-formate. Y 86%. F. e. s. L. A. Garpino, P. H. Terry, and P. J. Growley, J. Org. Ghem. 26, 4336 (1961). 

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