Photochemical Transformations, 75. The Azo/Nitrene Route to cis,cis‐Trialkyltriaziridines, 2^1b) Photolysis of syn‐Azo Azides of Defined Proximity – Attempts for N₃ → N₃X Ring Enlargement

Abstract

The as yet unknown route to triaziridines by the addition of nitrenes to the n side of the N = N bond is achieved intramolecularly by the photolysis (thermolysis) of syn-azo azide substrates with high proximity; the yields reflect the sterical (and possibly inductive) influences of the skeleton. The product composition is rather independent of the exciting light; intramolecular azo + azide energy transfer is assumed. The kinetic skeleton stabilization of the triaziridines permits the synthesis of 17 (18) by the thermolysis of 7 (8) at 200°C with the product composition deviating only marginally from that of the photolysis. Attempts towards enlargement of the triaziridines to N3X rings (X = CHR, 0, NR) lead exclusively to products of intramolecular fragmentation.The route to cis,cis-trialkyltriaziridines C as delineated in the preceding paper lb) encompasses the intramolecular cycloaddition of photochemically or thermally generated, unstabilized "discrete" secondary alkyl nitrenes B to unstabilized (dialkyl) azo units A. Yet, this route -with its obviousanalogy to the intramolecular three-membered ring construction by carbene') and nitrene3' addition to C = C bonds4) -has its intrinsic drawbacks: (i) Upon photoexcitation of secondary alkyl azides imine formation is generally very fast and may take place via discrete nitrenes or electronically excited a~ides*,~); (ii) N = N bonds are recognized as poor K~ components in cycloaddition reactions') with the consequence of even more severe stereoelectronic requirements for nitrene/N = N than e. g. for nitrene (carbene)/C = C additions; (iii) there is an omnipresent competitive process due to N2 elimination upon photoexcitation of azo systems, even though bi-and polycyclic azo compounds with skeletons similar to that of the azo azides considered for this study (Table 1) are found to be rather "reluctant" 7), the elimination of N2 being not generally a (very) fast process. Consequently, irrespective of the actual course of the nitrene generation, proper and as proximate and rigid as possible placement of the potential nitrene nitrogen atom with respect to the TC plane of the azo unit is mandatory for triaziridine formation. Thus, conformational and strain implications which often hamper intramolecular nitrene (carbene) additions to C = C bonds should be minimized'); (iv) intramolecular cycloaddition reactions between azide and N = N units yielding pentazolines should cause no complications, since the steric prerequisites for this ring formation are only met in severely distored excited states. In fact, such N5 rings have only been postulated as rate-determining transients in the unusually rapid thermolysis of o-azidoazobenzene~~). In this paper we present (i) the MMX-derived structural and energetic details of representative syn-azo azide substrates 1 -7 and of the respective triaziridines 11 -17; (ii) the results of the photolysis study on eight such syn-azo azide substrates (1,2,5,6-10; 3 and 4 are not yet available); (iii) some properties of the derived cis,cis-tria...

Mechanistic Studies of a Linear Trisazoalkane, a New Azimine, and a Bicyclic Triaziridine. Azoalkane Homolysis into Seven Fragments

“…A possible mechanism for the formation of azimine 5 during the synthesis of 1 is halogenation of the amino group of 3 or of the sulfamide nitrogen of 4 followed by displacement of the halogen by the azo group. However, since no mechanistic studies have been carried out, we cannot rule out 9 as an intermediate in the formation of 5 . The new azimine afforded both a picrate and a hydrogen iodide salt, selected bond lengths of which are shown below.…”

Small Rings by Azide Chemistry

“…107 These compounds were then irradiated in dilute solution to give triaziridines among other products. 108 For example, the azide 85 gave the triaziridine 86 (25%), a crystalline compound that could be purifi ed by sublimation (Scheme 6.34 ). The cage compounds 87 (X = CH, CMe, P and P = O) were prepared in an analogous way.…”

Isotriazene: A Surprisingly Stable Minimum on the N3H3 Surface

“…did speculate about the possibility of a “structure such as ...H 2 NNH + N - .” Nor have we uncovered a synthesis of an organic derivative of isotriazene. Organic derivatives of both c,t - and c,c -triaziridine have been synthesized and isolated, and triaziridine itself has probably been synthesized inside a silver-exchanged zeolite, so it is reasonable to speculate on the possibility of synthesizing derivatives of the more stable isotriazene. Substituents at N2 with appropriate electron-donating ability might be able to stabilize the charge on N2 and block the fragmentation reactions mentioned above.…”