Syntheses of azapolycyclic compounds by aminium radical routes: trapping of the radical intermediates

Abstract

Photolysis of three alkenyl nitrosamines in the presence of oxygen or bromotrichloromethane resulted in the interception of the intermediate C-radicals by these radical trapping agents and the reaction pathways were cleanly diverted leading to the formation of the nitrate esters or halides with pyrrolidine rings as the primary products. The exo-nitrates in the oxidative photolyses decomposed by secondary ionic pathways; these reactions were hydrolysis, nitrous acid elimination and a cleavage reaction (promoted by a β-amino group), among others. The efficiency of the cleavage reaction is controlled by a stereoelectronic factor that requires the participating bonds and the lone-pair nitrogen orbital be oriented in an antiperiplanar conformation. When such a conformation exists in a rigid or semiflexible framework, cleavage occurs extensively. However, in freely rotating acyclic systems, cleavage does not occur even when the required conformation can be attained. Only halides resistant to intramolecular nucleophilic displacement to form the aziridinium intermediates were isolated in the bromotrichloromethane trapping experiments. Other exo-halides underwent solvolysis via aziridinium ion intermediates.

Addition reactions of aminium radicals: oxidative and non-oxidative photoaddition of nitrosoamines to non-conjugated polyenes

“…Photoaddition of NND to tttCDT under nitrogen afforded 76% of syn-l-hydroxyimino-2-dimethylamino-trans,trunscyclododeca-5,9-diene (14) which was readily purified. The amino-oxime (14) was hydrolysed to give the corresponding ketone (15) which had been prepared previously.'…”

Chemistry of amidyl radicals: intramolecular reactivities of alkenyl amidyl radicals

“…The solution was made basic (pH 9), and was extracted with CH2C12 and chromatographed on alumina to give the first fraction, which was distilled at 84-85"C/5 Torr (1 Torr = 133. (32). The alcohol mixture (150 mg) was oxidized with a Jones' reagent for 20 min to give, after work-up, aminoketone 8 (90 mg); the ir, nmr, and mass spectra were identical with those of the authentic sample (32).…”

“…Successful use of BrCCl, as a radical trapping agent (32) led us to photolyze nitrosamide 3b in BrCCl, whereby single exobromolactam 17 was isolated in 89% yield. In the process, CC1,NO was also formed, as shown by the uv absorption (32) at 580 nm. The nmr spectrum became well separated on addition of Eu(fod),; decoupling experiments on this spectrum (see Experimental) clarified the coupling patterns of the protons.…”

“…Their configurations were clearly indicated by the N-CH and N-CH, protons at 3.90 and 2.82 pprn for anti-6 as compared to those at 4.65 and 2.89 pprn for syn-6. The ketolactam 7 was reduced with NaBH, to endo-and exo-hydroxylactams 10, and with LAH followed by Jones' oxidation to aminoketone 8, the structure of which was established previously (32). Enone oxime 11 could not be separated to its syn and anti isomers, but showed ir absorptions at 1670 and 1550 cm-' for a secondary amide and the chemical shifts of the olefinic protons at 6.3 and 5.8 pprn regions assignable to such conjugated oximes (33).…”

“…The required amides la-6a were prepared by the usual methods and described in the thesis (25). Nitrosation of amides followed published methods (9,32,38) using NaNO, in AcOH-Ac20 or N204 in CH2C12. In certain cases, the addition of N204 to the alkenyl bonds also occurred to give nitrosamides contaminated by such by-products.…”