AcOH-Catalyzed Rearrangements of Benzo[e][1,4]diazepin-2(and 3)-ones: Easy Access to 1,4-Dihydroquinazolines and Their Condensed Analogues

Presented herein is a novel synthesis of new 2-(quinolin-4-yl)-1,4-dihydroquinazoline systems 8, in which the acid-catalyzed rearrangement of spiro[benzo[e][1,4]diazepine-3,4'-quinolin]-2(1H)-ones generated in situ from 3-(2-aminophenyl)-5H-benzo[e][1,4]diazepin-2(1H)-ones 6 with acetone and alkylmethyl ketones has been realized as an important step. An attempt to synthesize isomeric 2-(2-aminophenyl)-5H-benzo[e][1,4]diazepin-3(4H)-one 6'a by hydrolysis of the corresponding N-{2-[5H-benzo[e][1,4]diazepin-3(4H)-on-2-yl]phenyl}acetamide 5'a led to a new heterocyclic system, 6-methyl-8,13-dihydro-13aH-quinazolino[4,3-b]quinazolin-5-ium 13a-carboxylate 14, as a result of an unexpected rearrangement. In addition, it is noteworthy that during the hydrolysis of N-{2-[5H-benzo[e][1,4]diazepin-2(1H)-on-3-yl]phenyl}acetamides 5, the not previously described 14-dihydro-5H-14,5a-(epimino[1,2]benzo)benzo[5,6][1,4]diazepin[2,1-b]quinazolin-6(7H)-ones 7 were unexpectedly obtained.

Synthesis of Chroman-2,4-diones via Ring-Opening/Ring-Closing Reaction Involving Palladium-Catalyzed Intramolecular Aryloxycarbonylation

Palladium-catalyzed aminocarbonylation of 3-iodochromone was studied in the presence of primary and secondary amines using atmospheric pressure of carbon monoxide as a carbonyl source. This procedure successfully provided a library of chromone-3-carboxamides and 3-substituted chroman-2,4-diones in 40 to 92% isolated yields. The reaction proceeded via highly chemoselective aminocarbonylation (up to 100%) in the presence of secondary amines by using monodentate or bidentate phosphine ligands. The tendency of 3-iodochromone substrate to undergo ANRORC rearrangement with N-nucleophiles was crucial to shift the reaction toward an unprecedented chemoselective carbonylative transformation, where a late-stage carbonyl insertion is favored concomitantly to the last ring-closure step. The proposed aza-Michael addition/ring-opening/intramolecular aryloxycarbonylation sequence showed compatibility, uniquely, to primary amines when XantPhos was used as a ligand. The solid-state structures of chromone-3-carboxamide (2a) and chroman-2,4-dione (3s) were undoubtedly established by single-crystal XRD analysis. A catalytic cycle was proposed to rationalize the formation of the two types of carbonylated compounds.

Lewis acid-promoted direct synthesis of isoxazole derivatives

Isoxazole derivatives were synthesized via a one-pot method utilizing 2-methylquinoline derivatives as template substrates, sodium nitrite as a nitrogen-oxygen source, and solely using aluminum trichloride as the additive. This approach circumvents the need for costly or highly toxic transition metals and presents a novel pathway for the synthesis of isoxazole derivatives.