Iminyls. Part 9. Intramolecular addition of an iminyl to an alkene

Abstract

Phenyl o-styrylphenyl iminyl, generated by oxidation of the corresponding O-carboxymethyloxime with persulphate and by thermolysis of the perester of that acid, cyclises to give a mixture of isoquinoline and 1H-isoindole derivatives. The intermediate radicals have been investigated by e.s.r. Chemistry, University of Aberdeen, Meston Walk, Old Aberdeen AB9 2UE, ScotlandPREVIOUSLY we reported that iminyls cyclised efficiently onto an adjacent aromatic ring, given favourable molecular geometry, although they did not react with benzene or substituted benzenes under ordinary conditions. We describe here a further intramolecular reaction of iminyls for which there is no intermolecular analogy. Although the parent iminyl (CH,=N*) does not react with liquid ethylene at 260 K, intramolecular addition of an iminyl onto an adjacent alkenyl group has now been observed.The iminyl (2; R = Ph) was generated by oxidation of the acids (1 ; R = Ph, X = H, R' = H and Me) with persulphate in boiling aqueous solution, and by decomposition of the corresponding perester (1 ; R = Ph, R' = H, X = OBut) in boiling benzene, both established routes to i m i n y l~.~ From the blue mixture obtained from the persulphate oxidation four products were separated. An intensely blue pigment was identified as the known isoindolyl derivative (10; R = Ph) (24%) the methylene analogue (10; R = H) of which we had previously obtained from phenyl o-tolyl iminyl and formaldehyde.s The phenyl analogue (10; R = Ph) was prepared from benzaldehyde and l-phenyl-lH-i~oindole.~ The other products were the red 2,3-diphenylindenone (14; R = Ph) (50/0) and two isomeric materials (C,H,,N).One of these was the diphenylisoquinoline 8 (4; R = Ph) (39%) and the other is tentatively assigned the isoindole structure (6;We consider that these products arise by (i) cyclisation [routes (a) and (b) Scheme 11 and (ii) hydrogen abstraction [route (c) Scheme 21 by the first-formed phenyl ostyrylphenyl iminyl (2; R = Ph). A measure of the competitive cyclisation to give 6-and &membered rings is given by the 4 : 3 ratio of (4; K = Ph) to (6 and 10; R = Ph). Significantly, in Scheme 1 the 1H-isoindole (6; R = Ph) is an intermediate en route to (10; R = Ph). The route to 2,3-diphenylindenone is less obvious but it probably involves the imine (1 1) as shown in Scheme 2. We have frequently isolated imines and their hydrolysis products, the corresponding ketones, from oxidations of iminoxyacetic acids (O-carboxymethyloximes) with p e r~u l p h a t e s .~*~*~ The source of abstractable hydrogen has not been fully established (formaldehyde?) but the occurrence of the reaction is not in doubt.A similar set of products was isolated when a solution of the t-butyl perester (1; R = Ph, R' = H, X = OBut) R = Ph) (6%).in benzene was heated under reflux. Yields were lower but products with %membered and &membered rings were again isolated. However, in this case 2,3-diphenylindenone was absent. Instead, o-styrylbenzophenone was isolated. This result is consistent with Scheme 2, the water and acid n...

Visible‐Light‐Mediated Generation of Nitrogen‐Centered Radicals: Metal‐Free Hydroimination and Iminohydroxylation Cyclization Reactions

“…Drawing inspiration from the work of Forrester,[ 12 ] Narasaka,[ 13 ] and Walton,[ 14 ] we speculated that appropriately functionalized O -aryl oximes could serve as general, bench-stable NCR precursors that could deliver iminyl radicals upon photoredox activation under mild conditions. [ 15 ] Such an approach would clearly benefit from the facile synthesis of aryl oximes, and we hoped that the high structural modularity of the O -aryl hydroxylamines would allow us to identify substrates that do not require the use of transition-metal-based photocatalysts.…”

Generation of Iminyl Radicals through Sulfanyl Radical Addition to Vinyl Azides

“…Generation of iminyl radicals is of interest especially in view of very recent reports of their utility in synthetic radical chemistry. Iminyl radicals have been proved to exhibit intramolecular cyclization reactions onto double bonds − and aromatic rings 2 as well as fragmentation reactions 4 to give nitrile products. These species have been formerly generated by thermolysis or photolysis of various N-substituted imine derivatives, by addition of carbon radicals to nitriles and, very recently, using radical-chain reactions of Bu 3 SnH with sulfanylimines 3 , N -benzotriazolylimines, and xanthic hydrazones …”

Microwave- and Thermally Promoted Iminyl Radical Cyclizations: A Versatile Method for the Synthesis of Functionalized Pyrrolines

“…Iminyl radical cyclizations occupy a central role in the growing field of nitrogen-centered radical chemistry . Seminal observations by Forrester were followed by Zard’s pioneering work and Weinreb’s contributions that rendered these transformations practical. Recently, developments in the areas of photoredox and transition-metal catalysis have inspired the discovery of several iminyl radical cyclizations that generate functionalized pyrrolines.…”