Stereoselective Synthesis of Pyrano[3,2‐c]‐ and Furano[3,2‐c]quinolines: Samarium Diiodide‐Catalyzed One‐Pot Aza‐Diels–Alder Reactions

Abstract

Three-component aza-Diels-Alder reactions involving aromatic aldehydes, aromatic amines, and dihydropyran or dihydrofuran are effectively catalyzed by samarium diiodide to afford pyrano[3,2-c]-or furano [3,2-c]quinolines in good yields and with high stereoselectivities. Either the cis or the IntroductionThe tetrahydroquinoline skeleton exists in many natural or synthetic biologically active materials, and its derivatives are widely applied in the pharmaceutical and biochemical fields.[1] Some of them, such as pyrano-and furanoquinolines, have attracted special attention as a result of their high degrees of structural diversity and wide spectra of biological actions.[2] The [4+2] cycloaddition reactions between N-arylimines (heterodienes) and dihydropyran or dihydrofuran (dienophiles) under Lewis acid catalysis conditions have long been recognized as one of the most convenient methods for the synthesis of quinolines of this type and have been explored for catalysts, scope, and applications.[3] However, most of the imines used as starting materials are unstable, which leads to difficulties in their isolation and purification. In this connection, much attention has been focused on three-component aza-Diels-Alder reactions involving aldehyde, amine, and either dihydropyran or dihydrofuran. A series of Lewis acids such as Ln-(OTf) 3 , [4] GdCl 3 , [5] molecular iodine, [6] TMSCl, [7] SbCl 3 , [8] and Selectfluor TM [9] have been found to be effective catalysts for this purpose. Normally, the process affords the products as mixtures of cis and trans isomers, in which the trans isomer is the major one in most cases. It is noteworthy that the use of Lewis acids as catalysts in one-pot reactions to prepare the tetrahydroquinolines stereoselectively with particular preference for the cis isomers has met with limited success in the past. Kobayashi [4a] has reported the formation of furano[3,2-c]quinoline with 62 % cis selectivity using (polyallyl)scandium trifylamide ditriflate as a catalyst. More recently, Yadav [9] has demonstrated the utility of Selectfluor TM as a catalyst to generate about 90 % yields of cis pyrano-and furanoquinolines. Therefore, it is still necessary to develop new and efficient catalysts for stereoselective syntheses of tetrahydroquinolines to make better use of this one-pot synthesis methodology.On the other hand, SmI 2 has served as a Lewis acid-type precatalyst and has been applied to a variety of reactions. [10] In our ongoing research into developing SmI 2 as a precatalyst in organic synthesis, [11] we investigated one-pot iminoDiels-Alder reactions of aldehydes and amines with dihydropyran or dihydrofuran in the presence of catalytic amount of SmI 2 . It was found that SmI 2 was effective for this process and that the stereoselective synthesis of pyrano[3,2-c]-and furano[3,2-c]quinolines could conveniently be effected through control of the reaction conditions. We now wish to report on these results. Results and DiscussionTo select favorable reaction conditions, we first examined the model re...

Scandium(III) Zeolites as New Heterogeneous Catalysts: [4+2]Cyclocondensation of in situ Generated Aryl Imines with Alkenes

“…Some of the so-formed adducts are known compounds, and hydroquinolines 5 a [38] 5 b, [39] 5 c, [40] 5 d, [41] 5 f, [42] 5 g [15] 5 h, [32] 5 I, [39] 5 l, [40] and 5 n + . Detailed experimental procedures for 5 a-r and for 4 a and NMR spectra of all new compounds are given in the Supporting Information.…”

“…It is worth noting that literature precedents for reactions with enol ethers often mentioned mixtures of diastereoisomers, with the cis isomer as a major product for Sm III , Ce IV , or Ti IV as the catalyst [15,16,32] but with the trans as the major product in the presence of Yb III , I 2 , TMSCl, or even 4-nitro- Ratio [c] cis/trans phtalic or phosphomolybdic acids. [37] The overall cis preference observed with Sc III zeolite whatever the "dienophile" could also be due to the spherical shape of the zeolite used (USY), favoring more or less spherical rather than extended transition states, especially in the stepwise mechanism (Scheme 5).…”

“…[12] Among them, the formal [4 + 2]cycloaddition reactions between N-arylimines acting as heterodienes towards dienophiles have long been recognized as one of the most convenient and rapid methods for the synthesis of (hydro)-quinolines. Usually performed under acidic conditions, such cycloadditions have been reported with various Lewis acid catalysts, such as bismuthA C H T U N G T R E N N U N G (III) bromide, [13] niobium(V) chloride, [14] samarium diiodide, [15] cerium(IV) ammonium nitrate, [16] magnesium perchlorate, [17] copper(II) bromide, [18] indium trichloride, [19] and lanthanide salts. [20] However, supported and reusable catalysts remained scarcely used despite obvious advantages, and only indium trichloride supported on polyaniline, [21] antimony chloride on hydroxyapatite, [22] Abstract:…”

FeCl3-Catalyzed Synthesis of 2-Methyl-4-Substituted-1,2,3,4-Tetrahydroquinoline Derivatives by the Imino Diels-Alder Reaction

“…Their structural assignment and the ratio of regioisomers of 8 and 9 were based on 1 H NMR spectroscopic data. The 1 H NMR spectrum of 8 showed 3 peaks on the benzene ring at δ 6.91(d, J = 7.8 Hz), 6.65 (t, J = 7.8 Hz), and 6.41 (d, J = 7.8 Hz), whereas 9 exhibited 3 peaks at δ 6.69 (d, J = 8.1 Hz), 6.57 (dd, J = 8.1, 1.8 Hz), and 6.44 (d, 1.8 Hz). p-Substituted aniline reacted smoothly with N-vinylpyrrolidinone to give the corresponding tetrahydroquinoline 11 in 84% yield, respectively (entry 7).…”

Tandem addition-cyclization reaction catalyzed by ytterbium chloride: An efficient one-step synthesis of 2-amino-4H-3,1-benzothiazine

“…Lanthanides are nontoxic and relatively abundant in nature, and the success in developing many useful reactions efficiently catalyzed by lanthanide compounds is attributed to the unique features of lanthanide centers such as high electrophilicity, variable metal ion radius and tunable coordination patterns. As a continuation of our interest in the applications of lanthanide-catalyzed carbon-nitrogen and carbon-phosphorus bond-forming reactions [32][33][34][35][36][37][38][39][40] for the construction of heterocycles, we investigated the effectiveness of lanthanide chlorides as catalysts for carbon-sulfur bond-forming reactions. Herein, a highly efficient process affording 2-amino-4H-3,1-benzothiazines by lanthanide chloride-catalyzed tandem addition-cyclization reaction of o-aminocinnamate and isothiocyanates is presented.…”