Nitrenes alkoxycarbonyl

Problems arise in the preparation of substituted l//-azepines with (alkoxycarbonyl)nitrenes as nitrene attack on a mono- or disubstituted benzene ring is not generally regioselective, and with toluene, 04 34-136139 144 o- and p-xy ienes,134-139 p-cresoi,134 chlorobenzene104-134 136 and biphenyl,104 136 mixtures of 1//-azepine-1-carboxylates of undetermined composition are produced. 

The same group expanded their study to see how well nitrenes derived from N-(alkoxycarbonyl) 0-(arenesulfonyl)hydroxyfamines 3i-o perform in a-amination of a,fi-unsaturated carljonyl compounds by aziridination. Good results are obtained when a,-unsaturated carboxylates and y-lactones are reacted with the amination reagents 3k, 31 and 3n in the presence of CaO. 

JV-Alkoxycarbonyl- and iV-arenesulfonyl-imines can be prepared by the reaction between pyridines and nitrenes, the latter being generated from the corresponding azides (72JOC2022, 64TL1733). Thermolysis of pyridinium iV-acylimines gives isocyanates and the parent heterocycle <79JCS(P1)446). 

Acyl nitrenes are highly reactive but unfortunately their precursors, acyl azides, are chemically reactive, e.g. they acylate amino groups. While sulfonyl- and alkoxycarbonyl azides are somewhat less reactive than acyla-zides, and the nitrenes derived from them are highly reactive (Lwowski, 1970 and for sulfonyl nitrenes see Abramovitch et al., 1981 and references therein), the azides must be irradiated in the UV, below 300 nm. Phos-phorylnitrenes are the most reactive nitrenes known and will insert into CH bonds in the presence of hydroxyl groups (Breslow et al., 1974). Again, photolysis occurs at ultraviolet wavelengths. 

Scheme 1.19 Sidewall functionalization of SWCNTs by [2+1]-cycloaddition of alkoxycarbonyl nitrenes obtained from azides.

Sidewall functionalization of SWCNTs was achieved via the addition of reactive alkyloxycarbonyl nitrenes obtained from alkoxycarbonyl azides. The driving force for this reaction is the thermally-induced N2 extrusion. The nitrenes generated attack nanotube sidewalls in a [2+l]-cycloaddition forming an aziridine ring at the tubes sidewalls (Scheme 1.19). 

Acyl azides which produce the nitrenes 3 and 4 upon photolysis are the most suitable for synthetic applications of cycloaddition reactions. Therefore, this subchapter will mainly deal with alkoxycarbonyl and aroyl nitrenes. 

Olefinic double bonds react with most nitrenes to form aziridines. However, alkoxycarbonyl nitrenes are not very suitable for making aziridines as they are too reactive, forming various C-H insertion products often resulting in the aziridine yield being low (an exception is given in Sch. 13) [23,24]. Furthermore under photolytical conditions, one-third of the nitrene is generated in the triplet state that reacts nonstereospecifically [25]. 

The outcome of the nitrene addition reaction depends on the type of 7i-bond involved. In contrast to electron deficient olefins [26] and nonpolar olefins forming aziridines, electron rich olefins react with alkoxycarbonyl nitrenes to give oxazolines (Sch. 14) [22]. The same type of cycloaddition reaction leading to the production of five-membered rings has also been observed with nitriles [27] (such as compound 35 in Sch. 14) and isocyanates [28] as illustrated in Sch. 15. 

Ethoxycarbonyl nitrene is able to add to compound 104a with a lower degree of stereoselectivity (d.e. 10%) compared with benzoylnitrene [22]. Nevertheless the addition of alkoxycarbonyl nitrene to unsaturated sugars such as compound 106 has been used in order to synthesize amino... 

Alkoxycarbonyl azides, which do not readily undergo the Curtius rearrangement, have a much richer triazoline and nitrene chemistry, the scope and theory of which are frilly discussed by Lwowski. Carb-ethoxynitrene may be generated by a-eliminations, c tiorudly assisted by ultrasound or PTC (Scheme 23). - ... 

The addition of alkoxycarbonyl nitrenes, generated photochemically from azides, to substituted dihydropyrans and tri-O-acetyl-D-glycal57"59 in alcoholic solution gave the products of alcoholysis 30 and 31-33 of the intermediate aziridines by a one-pot procedure59. The attack of the nitrene takes place mainly on the less hindered face of the double bond, but complete control of the diastereoselectivity was not accomplished even the ring opening of the aziridine can follow both anti and syn stereochemistry. 

The intramolecular aziridination of alkoxycarbonyl azides derived from ( )-5-hydroxymethyl-2(5//)-furanone, via thermal decomposition to nitrenes, gave the tricyclic compound 34 which was successively converted to the bicyclic compound 35. The aziridine ring opening with hydrazoic acid/ sodium azide ion of the aziridines 34 and 35 gives azido lactones 36 with the xylo configuration mixtures of xylo- and (y.w-forms were obtained by partial epimerization in equilibrating conditions and were easily separated60. 

Insertion into N—bonds by alkoxycarbonylnitrenes is a facile reaction, but is hampered by nucleophilic displacement of azide ion when alkoxycarbonyl azides are used as the nitrene precursor. Haf-ner obtained a 52% yield of phenylhydrazoformate, PhNHNH-COOC2H5, by thermolysis of ethyl azidoformate in aniline Aroyl azides have also been used Horner obtained a 14% yield of N-phenyl-iV -benzoylhydrazine by photolys ng benzoyl azide in aniline. With more nucleophilic amines, it is better to use the a-elimination route to alkoxycarbonylnitrenes . Using this method, yields of... 

Nitrenes generated photochemically or thermally from arenesulfonyl azides and alkoxycarbonyl azides add to the nitrogen atom of heteroaromatic bases to give the corresponding N-(substituted imines).20,21,50,64-69 However, the yields are usually low and the scope is severely limited. 

Dioxolanesetzensichunter Nitren-Einschiebung mit Azidoameisensaureesler zu 2-Alkoxycarbonyl-amino-1,3-dioxolanen (15 -25%) um198 ... 

Nitrenes addition Sidewalls Molecules with alkoxycarbonyl azide groups — —... 

Although the formation of aziridines from olefins and azides may not in all cases involve a nitrene intermediate, some recent literature reports of reactions of this type have for convenience been included in this section (see also the section on ring contraction). Alkoxycarbonyl nitrenes (R = Me or Et),... 

Ethoxycarbonylnitrene (generated photochemically from the azide) also reacts with 4-t-butylthian, affording a nearly 1 1 mixture of both cis- and trans-sulphimides. This non-stereoselectivity in the reaction of the nitrene is in marked contrast with that of the reaction of carbenes with the thian the thian reacts with both bis(alkoxycarbonyl)- and bis(diacetyl)-carbenes, giving the trans-yMes as the sole products (see Vol. 4, p. 112). Various sulphimides of cyclic sulphides, e.g. thians, cis- and frans-thiadecalins, oxathians, and dithians, can be prepared by treating the sulphides either with anilines and AT-chlorosuccinimide or with Bu OCl. In this reaction, the formation of (33 R = Bu , = /7-ClCjH4) with an equatorial... 

Enantioselective imidation of alkyl aryl sulfides with A -alkoxycarbonyl azides as a nitrene precursor is effected by using (OC)Ru(salen) complex as catalyst. The steric and electronic nature of the Af-alkoxycarbonyl group strongly affect the enantioselectivity and the reaction rate. In a systematic and well-executed study of ligand effects on Lewis-acid-catalyzed Diels-Alder reaction, it has been shown that the attachment of aromatic a-amino acid ligands to copper(II) ions leads to an increase in the overall rate of the Diels-Alder reaction between 3-phenyl-l-(2-pyridyl)-2-propene-l-one (Din) and cyclopentadiene... 

Tamura, Y., Uchida T., Katsuki, T. Highly enantioselective (OC)Ru(salen)-cata-lyzed sulfimidation using N-alkoxycarbonyl azide as nitrene precursor. Tetrahedron Lett. 2003, 44(16), 3301-3303. 

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