Scandium Pentafluorobenzoate-Catalyzed Unexpected Cascade Reaction of 2-Aminobenzaldehydes with Primary Amines: A Process for the Preparation of Ring-Fused Aminals

Abstract

An unexpected cascade reaction of 2-aminobenzaldehydes with arylamines catalyzed by scandium pentafluorobenzoate [Sc(Pfb)3] was reported as a facile strategy for the efficient synthesis of a novel class of polycyclic ring-fused aminals N-substituted-6,7,11b,13-tetrahydro-6,12-[1,2]benzenoquinazolino[3,4-a]quinazolin-13-amines 1. Under similar conditions, a series of the analogues of Tröger's base, 13-substituted-5,6,11,12-tetrahydro-6,12-epiminodibenzo[b,f][1,5]diazocines 2 were obtained when the arylamines were replaced by methanamines. A possible mechanism for the formation of 1 and 2 was proposed.

Proton-Mediated Practical Synthesis of McGeachin-Type Bisaminals

“…Various racemic McGeachin-type bisaminals were prepared from aromatic amines under the optimal conditions (Scheme 2). Compared with the strategy of Yu and Wang, 12 the reactions of arylamines exhibited an excellent chemoselectivity toward A 2 B condensation and afforded a variety of target products. Anilines bearing electron-donating methoxy groups 1a-c, regardless of the number and position (meta or para), as well as the methylthio group 1d, readily underwent the condensation with 2a to afford expected bisaminals 3a-d in 75-80% isolated yields.…”

“…SYNTHESIS0 0 3 9 -7 8 8 1 1 4 3 7 -2 1 0 X Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart 2021, 53, 2828-2840 (Scheme 1a). 12 One key to overcome this problem is to use N-functionalized 2-aminoarenecarbaldehydes, for example, changing the free NH 2 group to phosphanimine (N=PPh 3 ), 13 sulfonamide (NHSO 2 R), 14 or alkylamino (NHR) groups. 1b,15 Guided by this concept, Sridharan and co-workers successfully obtained McGeachin-type bisaminals in high yields through Yb(OTf) 3 -catalyzed A 2 B condensations between 2-(propargylamino)benzaldehydes and arylamines (Scheme 1b).…”

“…For example, in Yu and Wang's scandium pentafluorobenzoate catalyzed synthesis, the reactions of arylamines did not afford A2B condensation products, but coupling products of arylamines with trimers of 2aminoarenecarbaldehydes (Scheme 1a). 12 One key to overcome this problem is to use N-functionalized 2aminoarenecarbaldehydes, for example, changing the free NH2 group to phosphanimine (N=PPh3), 13 sulfonamide (NHSO2R), 14 Template for SYNTHESIS © Thieme Stuttgart • New York 2021-04-23 page 2 of 13…”

“…Various racemic McGeachin-type bisaminals were prepared from aromatic amines under optimal conditions (Table2).Compared with Yu and Wang's strategy,12 the reactions of arylamines exhibited an excellent chemoselectivity toward A2B Template for SYNTHESIS © Thieme Stuttgart • New York 2021-04-23 page 4 of 13…”

Lanthanum Pentafluorobenzoate-Catalyzed Aerobic Oxidative Olefination of Benzylamines with 2-Methylquinoline through Deamination and C–H Bond Functionalization

“…Alternatively, the aldehyde might condense efficiently with benzylamine (path b) to form N-benzylidene-1phenylmethanamine in the presence of La(Pfb) 3 , which is known to be an excellent catalyst for aldehyde-amine condensation reactions. 9,16 In this reaction, the consumption of aldehyde promotes the further oxidation of benzylamine to benzaldehyde, and the generated N-benzylidene-1-phenylmethanamine further reacted with 2-methylquinoline to afford the final product and release benzylamine in the meantime.…”