A useful tandem reaction via the Heyns rearrangement and Pictet–Spengler reaction was developed which ensured the synthesis of complex N-heteropolycycles containing tetrahydro-β-carboline with high yield (up to 96%) and dr (99 : 1).

A three component reaction with two different ketones and aromatic amines was firstly investigated. The difference in reactivity between ordinary ketones and ketone esters allowed for the production of 1,2-DHQs efficiently. The possible Skraup reaction with 2 equiv. of the same ketones was prohibited due to the fast formation of imines.

Av ariety of C3-, C6-, C8-and C13-functionalized 1,2-dihidroquinolines (1,2-DHQs)h ave been prepared through post-modification of simple 1,2-DHQs by regioselective Friedel-Crafts alkylations. Several commonly used electrophiles such as 3-indolylmethanolderivatives, nitroolefins, 1,4-benzoquinones, aromatic aldehydes and ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline were rationally used to afford the corresponding1 ,2-DHQs with high yield and regioselectivity.T he regioselectivity of the reaction appears to be governed by the substituents of the 1,2-DHQ substrates.1,2-Dihydroquinolines (1,2-DHQ) with various substituents aroundi ts core structure have increasingly gained much attention due to their intriguing pharmacologically and biologically properties. For instances, 1, 2-DHQs were widely used as antibacterial, [1] antitrypanosomal, [2] antioxidant [3] anda ntidiabetic agents, [4] anti-juvenile hormonei nsecticides, ( Figure 1). Meanwhile, they are efficient antioxidants [5] used as preservatives in animal nutriments, in vegetables, in animal oils and in rubber. Moreover,o ther applications are also involved such as linkers for solid-phase organic synthesis, [6] as the core in ferromagnetic compounds. [7] Accordingly,anumber of synthetic methods of 1, 2-DHQs have been disclosed.In general, traditional procedures are laborious, low yielding, and requires pecial synthetic precursors. Recently,e fficient strategies toward the synthesis of dihydroquinolines have been focusedo nac atalytic version. For example, transition metals such as palladium, [8] ruthenium,s ilver,a nd gold catalyzed reactions of anilines with alkynes, [9] (Scheme 1a); scandium triflate, [10] silicotungstic acid, [11] HNO 3 , [12] iodine, [13] zeolite, [14] MgBr 2 and Li 2 CO 3 , [15] organo-catalyst [16] catalyzed reactions of anilines with ketones and other miscellaneous methodsw ith specific substrates [17] (Scheme 1a). Generally,t hese methods were mainly designed on the basis of heterocyclic moiety formation, startingf rom the respectivef unctionalizeda nilines. While these approaches focus on the constructiono ft he ring structure, post-functionalization of the pre-existing 1,2-DHQ skeletons is also highly valuable.Recently,o ur group reporteda ne fficient way of forming the aza-ortho-xylylene (AOX) by dearomatization of 1,2-DHQ with catalytic Brønsted acid. [18] The resulting intermediate formed in situ could be efficientlyt ransformed with Hantzsch ester (HEH) or indoles to the corresponding tetrahydroquinolines (THQs) with high yields and enantioselectivities. Moreover,w ef ound that the 1,2-DHQ substrate could react smoothly with aromatic iminest hrough step-controlled Povarov reaction to afford Figure 1. Selected examples of the applicationsof1 ,2-DHQs.Scheme1.Strategies to obtain 1,2-DHQs.[a] J.