The aza-xylylene Diels–Alder approach for the synthesis of naturally occurring 2-alkyl tetrahydroquinolines

Synthesis and Anticancer Activity of 3,4-Diaryl-1,2-dihydro- and 1,2,3,4-Tetrahydroquinolines

Tetrahydroquinolines are key structures in a variety of natural products with diverse pharmacological utilities and other applications. A series of 3,4-diaryl-5,7-dimethoxy-1,2,3,4-tetrahydroquinolines were synthesized in good yield by reacting 3-aryl-5,7-dimethoxy-2,3-dihydroquinolin-4-ones with different Grignard reagents followed by the dehydration of the intermediate phenolic compounds. Subsequent reduction and deprotection were carried out to achieve the desired tetrahydroquinolone moiety. The lead compound 3c showed low micromolar inhibition of various cancer cell lines. Demethylation under different reaction conditions was also investigated to afford the corresponding monohydroxy analogues.

Inverse Electron Demand Diels Alder Reaction of Aza-o-Quinone Methides and Enaminones: Accessing 3-Aroyl Quinolines and Indeno[1,2-b]quinolinones

We have developed a Diels Alder cycloaddition route toward 3-aroyl quinolines from enaminones and in situ generated aza-o-quinone methides. The reaction was found to be general with a range of substituted enaminones and aza-o-quinone methides, and we could validate the applicability of the methodology in gram scale. We also demonstrated a one-pot strategy toward 3-acyl quinolines starting from the corresponding aliphatic ketones. Finally, we utilized the 3-aroyl quinolines for synthesizing indeno[1,2-b]quinolinones via a Pd-catalyzed dual C-H activation approach.

Aza-ortho-Quinone Methide and Its Conjugated Acid: Reactivity, Stability and Acidity

Aza-o-quinone methides and their conjugated acids are reactive drug metabolites that might react with nucleophilic sites of DNAs and proteins to cause cancer or immune responses, and their reactivity with water is the key information to judge if these metabolites are harmful in living systems. For the first time, aza-o-quinone methide (1) and its conjugated acid (2) are observed by laser flash photolysis, and their reactivity, stability and acidity in water are determined.

Facile synthesis of 1,2,4,5-tetrahydro-1,4-benzodiazepin-3-ones via cyclization of N-alkoxy α-halogenoacetamides with N-(2-chloromethyl)aryl amides

A facile and efficient cyclization of N-alkoxy α-halogenoacetamides with N-(2-chloromethyl)aryl amides has been achieved for rapid access to 1,2,4,5-tetrahydro-1,4-benzodiazepine-3-one derivatives (up to 95% yield). The intriguing features of this intermolecular cyclization include its mild reaction conditions and easy handling for scalable synthesis.

An organic-base catalyzed asymmetric 1,4-addition of tritylthiol to in situ generated aza-o-quinone methides at the H2O/DCM interface

Highly enantioselective organocatalytic Michael addition of tritylthiol to N-o-QM intermediates generated in situ at the H₂O/DCM interface is presented.

Recent advances in the application of Diels–Alder reactions involving o-quinodimethanes, aza-o-quinone methides and o-quinone methides in natural product total synthesis

This review summarizes recent advances in Diels–Alder reactions involving o-QDMs, o-QMs and aza-o-QMs. The power and potential of this strategy in organic synthesis and natural product total synthesis is highlighted.

Base-mediated [2 + 4] cycloadditions of in situ formed azaoxyallyl cations with N-(2-chloromethyl)aryl amides

A base-mediated [2 + 4] annulation of in situ formed azaoxyallyl cations with in situ generated aza-oQMs has been realized.

[4 + 3] Cycloadditions with Bromo-Substituted Morita-Baylis-Hillman Adducts of Isatins and N-(ortho-Chloromethyl)aryl Amides

Efficient construction of a challenging aza-spirocycloheptane oxindole scaffold is reported through an unprecedented [4 + 3] cycloaddition reaction with bromo-substituted Morita-Baylis-Hillman adducts of isatins and N-(ortho-chloromethyl)aryl amides. Both reactive intermediates, the allylic phosphonium ylides and aza-o-quinone methides, were in situ generated, chemoselectively facilitated by a Lewis base and Brønsted base, respectively.

An intramolecular C-N cross-coupling of β-enaminones: a simple and efficient way to precursors of some alkaloids of Galipea officinalis

2-Aroylmethylidene-1,2,3,4-tetrahydroquinolines with the appropriate substituents can be suitable precursors for the synthesis of alkaloids from Galipea officinalis (cuspareine, galipeine, galipinine, angustureine). However, only two, rather low-yielding procedures for their synthesis are described in the literature. We have developed a simple and efficient protocol for an intramolecular, palladium or copper-catalysed amination of both chloro- and bromo-substituted 3-amino-1,5-diphenylpent-2-en-1-ones leading to the above-mentioned tetrahydroquinoline moiety. The methodology is superior to the methods published to date.

Au-catalyzed intramolecular annulations toward fused tricyclic [1,3]oxazino[3,4-a]indol-1-ones under extremely mild conditions

We report a general and efficient method for the rapid generation of tricyclic [1,3]oxazino[3,4-a]indol-1-ones under extremely mild conditions.

An enantioselective approach to 2-alkyl substituted tetrahydroquinolines: total synthesis of (+)-angustureine

A simple and highly efficient synthetic approach to enantiopure 2-alkyl substituted tetrahydroquinoline 1 skeleton from aldehydes as starting materials and its application to the total synthesis of (+)-angustureine 2 is described.

N-heterocyclic-carbene-catalyzed synthesis of 2-aryl indoles

A convergent and efficient transition-metal-free catalytic synthesis of 2-aryl-indoles has been developed. The interception of a highly reactive and transient aza-ortho-quinone methide by an acyl anion equivalent generated through N-hetereocyclic carbene catalysis is central to this successful strategy. High yields and a wide scope as well as the streamlined synthesis of a kinase inhibitor are reported.

Enantioselective annulations for dihydroquinolones by in situ generation of azolium enolates

A convergent, catalytic asymmetric formal [4 + 2] annulation for the synthesis of dihydroquinolones has been developed. Carboxylic acids can be employed as precursors to NHC enolates through an in situ activation strategy. Simultaneous generation of a reactive aza-o-quinone methide under the basic conditions employed for NHC generation leads to a dual activation approach.

Imino Diels–Alder reaction — An efficient synthetic protocol for 2-methyl-4-substituted tetrahydroquinolines catalyzed by copper dipyridine dichloride

For the first time, copper dipyridine dichloride (CuPy2Cl2) is used as an efficient and reusable catalyst for the imino Diels–Alder reaction of para-substituted anilines with N-vinylpyrrolidinone, N-vinylcarbazole, and N-vinylcaprolactam in acetonitrile to afford the corresponding 2-methyl-4-substituted-1,2,3,4-tetrahydroquinoline derivatives in excellent yields with good purity. The products were characterized by FTIR,1H NMR,13C NMR, MS, and elemental analysis.

Highly diastereoselective addition of alkynylmagnesium chlorides to N-tert-butanesulfinyl aldimines: a practical and general access to chiral alpha-branched amines

The addition of alkynylmagnesium chlorides to N-tert-butanesulfinyl imines proceeded with a remarkably high diastereoselectivity (dr > 13:1, mostly diastereopure), and with a general scope of both reaction partners. The high dr translated into simplified purification and higher optical purity for the synthesis of a wide array of chiral alpha-branched amines. The alkyne functionality also provides a multitude of opportunities for further synthetic transformations. The short asymmetric synthesis of (+)-angustureine 7 and (-)-cuspareine 10 was realized with use of this approach.