Solid-phase synthesis of 3,4-dihydroquinazoline derivatives

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.

Triflic anhydride mediated synthesis of 3,4-dihydroquinazolines: a three-component one-pot tandem procedure

A one-pot three-component tandem reaction involving a key Pictet-Spengler-like annulation step has been developed, providing an efficient method for the synthesis of 3,4-dihydroquinazolines in moderate to good yields from amides, aldehydes, and amines. The multicomponent triflic anhydride mediated reaction tolerates the installation of numerous functional groups, affording extensive diversity about the heterocyclic scaffold.

Synthesis of dihydroquinazolines from 2-aminobenzylamine: N 3 -aryl derivatives with electron-withdrawing groups

The sequential N-functionalization of 2-aminobenzylamine (2-ABA) followed by cyclodehydration allowed for a straightforward and efficient synthesis of 3,4-dihydroquinazolines with N-aryl substituents bearing electron-withdrawing groups. The sequence involves an initial S_NAr displacement, N-acylation and MW-assisted ring closure. Remarkably, the uncatalyzed N-arylation of 2-ABA led to the monosubstitution product using equimolar amounts of both reagents. The individual steps were optimized achieving good to excellent overall yields of the desired heterocycles, avoiding additional protection and deprotection steps. A mechanistic interpretation for the cyclodehydration reaction promoted by trimethylsilyl polyphosphate (PPSE) is also proposed on the basis of literature data and our experimental observations.

Palladium-catalyzed selective synthesis of 3,4-dihydroquinazolines from electron-rich arylamines, electron-poor arylamines and glyoxalates

Palladium-catalyzed selective synthesis of various 3,4-dihydroquinazolines from electron-rich arylamines, electron-poor arylamines and glyoxalates was developed.

Syntheses of 3,4- and 1,4-dihydroquinazolines from 2-aminobenzylamine

A straightforward strategy for the synthesis of dihydroquinazolines is presented, which allows for the preparation of 3,4- and 1,4-dihydroquinazolines with different substitution patterns from 2-aminobenzylamine (2-ABA) as common precursor. The required functionalization of both amino groups present in 2-ABA was achieved by different routes involving selective N-acylation and cesium carbonate-mediated N-alkylation reactions, avoiding protection/deprotection steps. The heterocycles were efficiently synthesized in short reaction times by microwave-assisted ring closure of the corresponding aminoamides promoted by ethyl polyphosphate (PPE).

Benzhydrylamines via base-mediated intramolecular sp(3) C-arylation of N-benzyl-2-nitrobenzenesulfonamides--advanced intermediates for the synthesis of nitrogenous heterocycles

N-Benzyl-2-nitrobenzenesulfonamides underwent base-mediated intramolecular arylation at the benzyl sp(3) carbon to yield benzhydrylamines. The presence of electron withdrawing groups on the aromatic ring of the benzyl group was required to facilitate the C-arylation. Unsymmetrically substituted benzhydrylamines are advanced intermediates toward nitrogenous heterocycles, as exemplified in the syntheses of indazole oxides and quinazolines.

Copper-catalyzed activation of α-amino peroxy and hydroxy intermediates to iminium ion precursor: an access to C4-substituted 3,4-dihydroquinazolines via oxidative cross coupling strategy

A simple and straightforward approach to access C4-substituted-3,4-dihydroquinazolines has been achieved, where copper-catalyzed activation of α-amino peroxide and hydroxide intermediates to iminium ion precursors has been realized as an important step. Reactions of these intermediates with alkynes, indoles, pyrrole, and silylenol ether afforded the structurally diverse C4-substituted-3,4-dihydroquinazoline derivatives in good yields.

Synthesis of quinazolines from N-(2-nitrophenylsulfonyl)iminodiacetate and alpha-(2-nitrophenylsulfonyl)amino ketones via 2H-indazole 1-oxides

Base-catalyzed rearrangement of 2H-indazoles 1-oxides, prepared by tandem carbon-carbon followed by nitrogen-nitrogen bond formations from easily accessible N-alkyl-2-nitro-N-(2-oxo-2-aryl-ethyl)-benzenesulfonamides using glycine, 2-nitrobenzenesulfonyl chlorides, and bromo ketones/acetates, yielded high purity quinazolines.

N,N-Bond-Forming Heterocyclization: Synthesis of 3-Alkoxy-2H-indazoles

A one-step heterocyclization of o-nitrobenzylamines to 3-alkoxy-2H-indazoles is reported. The electronic nature of the nitrophenyl group, the steric and electronic nature of the R1-functionalized benzylic amine, and the nature of the alcoholic solvent affect the efficiency of this heterocyclization reaction (approximately 40-90%).

The recent impact of solid-phase synthesis on medicinally relevant benzoannelated nitrogen heterocycles

Benzoannelated heterocycles such as benzodiazepines and indoles can be prepared efficiently through cyclization on solid supports, although no single approach is currently universal for the preparation of all benzoannelated N-heterocycle chemistries. In this review, a number of synthetic strategies for the generation of benzoannelated nitrogen heterocycles using resin-bound substrates have been described. Classical heterocycle forming reactions such as the Fischer indole, the Bischler-Napieralski tetrahydroisoquinoline, the Pictet-Spengler tetrahydro-beta-carboline, the Tsuge, the Nenitzescu and the Richter cinnoline reaction are presented. In addition, the Heck, Sonogashira, Wittig, Diels-Alder, and olefin metathesis reactions have been also used. Multicomponent reactions such as the Grieco three-component assembly have been exploited for the synthesis of heterocycles. Cyclative cleavage from the solid support is particularly suitable for the synthesis of heterocycles while particular emphasis has been focused on the synthesis of libraries and the use of combinatorial chemistry techniques. In addition, the most relevant pharmacological properties of benzoannelated nitrogen heterocycles are included.

Novel strategies for solid-phase construction of small-molecule combinatorial libraries

During the past decade we witnessed a rapid advance in the new field of chemical science, combinatorial chemistry. The pharmaceutical industries invested heavily in accelerating the development of this new technology. As a result, it has become an extremely important tool in lead identification and optimization in current pharmaceutical research. It also quickly crossed the boundaries of the original chemical discipline and demonstrated great potential in many other important areas, such as searching for novel and highly efficient catalysts and superconductive material. Researchers from both academic and industrial laboratories have directed great effort towards the development of novel strategies for combinatorial synthesis.