Curtius rearrangement Subject

An alternate route to substituted tetrahydrobenzazepines (Scheme 33) commenced with the Michael addition of the ester 351 to acrylonitrile in the presence of Triton B, and the intermediate cyanoester was converted to 352 by reduction of the ester function with lithium borohydride and O-benzylation (168). Base-induced hydrolysis of the nitrile group of 352 delivered the corresponding acid, which was transformed to 353 via a Curtius rearrangement. Subjection of 353 to a modified two-step Tschemiac-Einhom reaction involving AMiydroxymethyla-tion and subsequent acid-catalyzed cyclization gave 354. 

An extensive review of the chemistry of aliphatic and aromatic azides is given by Boyer and Canter [167] and Gray [168]. Organic azides are subject to various reactions such as the Bergmann degradation and the synthesis of peptides, the well known Curtius rearrangement, the Darapsky synthesis of a-aminoacids [169], for synthesis of triazoles [170], tetrazoles ( Schmidt reaction ) [169] and [171] etc. These reactions lie beyond the scope of the present book. 

A versatile route to p-substituted tryptophan esters was developed beginning with condensation of an indole, an aldehyde and Meldrum s acid. The condensation products can be solvolyzed to half esters and then subjected to Curtius rearrangement. <95TL2057>... 

This product, the acid azide, was subjected to the same kinds of Curtius rearrangement conditions as described above. 

N-oxide 220, which with acetic anhydride afforded the acetate 22L Treatment of 221 first with KaCOs/MeOH and then with SOCI2 led to the formation of chloride 222. Reaction of 222 with A -cyanomethylpyrrolidine gave the quaternary salt 223, which was, without isolation, converted into aldehyde 224 by treating first with f-BuOK and then with oxalic acid. Oxidation of 224 with pertrifiuoroacetic acid and then further oxidation of the N-oxide product with KMn04 gave the carboxylic acid 225. This compound was subjected to the Yamada modification of the Curtius rearrangement, then hydrolysis, to provide the amine 226. Treatment of 226 with... 

Oxabicyclo[3.2.1]oct-6-en-2-ones are also available from this chemistry, as illustrated in Scheme 30. Treatment of 84 with sodium methoxide and then lithium hydroxide, followed by subjecting the resulting acid to the standard Curtius rearrangement conditions, results in the formation of 8-oxabicyclo[3.2.1]oct-6-en-2-one (85) in 52% yield. Racemic 85 has been used by Vogel in a stereoselective synthesis of the P-C-hexopyranoside 86. ... 

From CFa-COCl + NaNa- CFj CO Na- -CFs NCO. Curtius rearrangement of iri-fluoroacetyl azide, which tends to detonate when subjected to thermal or mechanical shock, was effected at 120 °C in CHCl, the isocyanate thus obtained was contaminated with up to 25%ofCF,-N CF,.> ... 

They commenced their efforts by subjecting the cyclohexanone 84 to a Fischer indoUzation to furnish indolenine 85. A Curtius rearrangement and a hydrolysis protocol then converted the carboxylic acid to amine 86, which undergoes cyclization during the course of the reaction to render tetracychc pyrroloindole 82. 

And last, but not least, Fu et al. [21] reported that the planar-chiral heterocycle 45d catalyzed the enantioselective addition of hydrazoic acid to ketenes. This result in the formation of an acyl azide intermediate, which then can be subjected to Curtius rearrangement to supply a straightforward stereoselective access to chiral amines. As can be seen from Scheme 3.26, amine derivatives 56 were obtained in... 

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