Diels carbolines

The inverse electron demand Diels-Alder reaction has also been used to provide expedient access to unnatural 6-carboline alkaloids from 1,2,4-triazines, prepared by microwave-assisted MCR [92]. One-pot reaction of an acyl hydrazide-tethered indole 73, 1,2-diketone and ammonium acetate in acetic acid provided triazines 74 (see Sect. 3.2, Scheme 22), bearing an electron-rich dienophilic indole moiety (Scheme 31). By carrying out the... 

A semiempirical AMI study of the inverse-electron-demand Diels-Alder reaction of 4-substituted 6-nitrobenzofurans with enol ethers and enamines favours a stepwise mechanism involving short-lived diradical intermediates. The inverse-electron-demand intermolecular Diels-Alder reactions of 3,6-bis(trifluoromethyl)-l,2,4,5-tetra-zine with acyclic and cyclic dienophiles followed by the elimination of N2 produce 4,5-dihydropyridazines, which cycloadd further to yield cage compounds. The preparation of jS-carbolines (90) via an intramolecular inverse-electron-demand Diels-Alder... 

A method was developed for preparation of the tetracyclic carboline alkaloids iso-canthine, isocanthin-6-one and l-methylisocanthin-3-one by an intramolecular hetero-Diels-Alder reaction. For example, oxime 317 in sulfolane at 285 °C afforded isocanthine 318 in 8% yield (equation 137) . 

Manzamine alkaloids can be isolated from marine sponges. They often contain /3-carboline. This group has a diverse range of bioactivities. It also has its own way of establishing its structures. An intramolecular Diels-Adler reaction for manzamines has been proposed. The a is bisdihydropyridine (derived probably from amonia), and the (3 is intramolecular cycloaddition in a pentacyclic... 

Pyrrolo[2,3- ]pyridinones, 59, undergo an inverse electron demand Diels-Alder reaction with ethyl vinyl ether to generate 6-aza-5-carboline products in excellent yields but low stereoselectivity (Equation 4) <1997S73>. 

Imino Diels-Alder reactions.1 The cycloaddition of dihydro-p-carbolines with... 

Langlois and co-workers (82CC1118 85JOC961) succeeded in the total synthesis of vindrosine (46) and vindoline (47) by the imino Diels-Alder cycloaddition using dihydro-)3-carbolines and the diene shown in Scheme 5. 

A similar imino Diels-Alder reaction between dihydro-)9-carboline 30 and diene 31 afforded three products (33,35, and 37) (total yield 88%), which were directly alkylated to afford the 7-methoxyindoloquinolizidine derivative 39 as... 

A new and very neat synthesis of evodiamine and rutaecarpine is described by the authors as a retro mass spectral synthesis , since the original conception was derived from the mode of fragmentation of these alkaloids in the mass spectrometer this involves a familiar retro Diels-Alder fission of ring c. Evodiamine (16a) was thus constructed by a 27r + 47r cycloaddition of 3,4-dihydro-/8-carboline with the keteneimine (17), prepared in situ by elimination of sulphur dioxide from the sulphinamide anhydride (18) (Scheme 7). When the anthranilic acid derivative (19) was used the product was rutaecarpine (20) itself, the initially formed dihydro-... 

A novel tandem Pictet-Spengler/intramolecular Diels-Alder sequence has been used to prepare carboline derivatives. Reaction of imine 137 with maleic anhydride in CH2CI2 provided cycloadduct 140 in 60-80% yields (Scheme 25) (02TL203). The... 

Two other intramolecular Diels-Alder reactions focus on concurrent formation of the C(5)-C(10) and C(8)-C(9) bonds (135-138). Martin and coworkers at the University of Texas at Austin (135, 136) found that Lewis acid catalysis of 169 provided the desired diastereomeric product, 170 (Scheme 12) the stereochemical consequences of cyclization of 169 was investigated with respect to the A3 stereochemistry, demonstrating maximum selectivity (8 1), over the C(5) epimer, when the A3 olefin was cis (136). A subsequent extension of this method by Martin resulted in the introduction of an alkoxymethylene group to C(6) of 170, thus setting up intermediate 170 for attachment of the P-carboline ring system (136). The... 

The canthines are a tetracyclic subclass of j8-carboline alkaloids bearing an additional D-ring. Members of the canthine family have been shown to have pharmacological activity, including antifungal, antiviral, and antitumor properties. In 2003 Lindsley and coworkers described a microwave-mediated procedure for one-pot synthesis of the basic canthine skeleton [122]. The key step is an inverse-electron demand Diels-Alder reaction and subsequent chelotropic expulsion of N2, a reaction that can be achieved after a three-component condensation of an acyl hydrazide-tethered indole with a 1,2-diketone and excess ammonium acetate to form a triazine (Scheme 10.61). 

Application of Diels-Alder Reactions with 3-Vinytindoles in the Synthesis of P and y-Carboline Alkaloids... 

Snyder S A, Vosburg D A et al (2000) Intramolecular hetero Diels-Alder routes to g-carboline alkaloids. Tetrahedron 56 5329-5335... 

The structural dissection of the lavendamycin molecule 40 revealed a quinolinequinone (AB) and p-carboline (CDE) framework. Both these units are historically known and numerous methodologies for them have been formulated. It was therefore, hoped that the synthetic efforts towards 40 would not pose much difficulties. The synthetic tactics towards 40 revolve around the Bischler-Napieralski reaction between p-methyltryptophan and quinaldic acid to construct ring C, and in the process, bridging the two subunits. However, Roger s group preferred to extend the inverse electron demand Diels-Alder reaction, successfully demonstrated for streptonigrin, to the synthesis of lavendamycin. 

Hoomaert and colleagues synthesized a-carbolines and P-carbolinones via the intramolecular Diels-Alder cycloaddition of 2(17/)-pyrazinones (Scheme 27, equations 1, 2)... 

This chapter has presented an abundance of material on indole-carbazole-carboline syntheses that used the venerable Diels-Alder reaction in ways that would bring joy to Otto Diels and Kurt Alder. 

The tandem acylation and intramolecular Diels—Alder reaction of furan installed on the tetrahedron-P-carboline skeleton produced bridged polycyclic alkaloid-like products (13JOC9738). 

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