Pyrano- -indole-3-one

Pyrano[3,4-b]indol-3-ones are the most useful equivalents of the indol-2,3-quinodimethane synthon which are currently available for synthetic application. These compounds can be synthesized readily from indole-3-acetic acids and carboxylic anhydrides[5,6]. On heating with electrophilic alkenes or alkynes, adducts are formed which undergo decarboxylation to 1,2-dihydro-carbazoles or carbazoles, respectively. 

Pyrano[3,2-g]benzoxazine, dihydrosynthesis, 3, 714 Pyranobenzoxazines synthesis, 6, 190 Pyranobenzoxazoles mass spectra, 3, 615 Pyrano[2,3-a]carbazoles synthesis, 4, 235 Pyrano[2,3- 6]carbazoles synthesis, 4, 235 Pyrano[3,2-a]carbazoles synthesis, 4, 235 Pyranochromones synthesis, 3, 821 Pyranochromones, dihydrosynthesis, 3, 81 817 Pyranocoumarins crystal data, 3, 623 mass spectra, 3, 610 Pyranodipyranones synthesis, 3, 794 Pyrano[3,2-6]indol-4-ones synthesis, 4, 302 Pyran-2-ol, dihydrodehydration, 3, 762 Pyran-2-ol, 3-methyltetrahydro-synthesis, 3, 775 Pyran-2-ol, tetrahydro-6-substituted synthesis, 3, 775 Pyran-4-ol, tetrahydro-IR spectra, 3, 594 Raman spectra, 3, 594 Pyranols, tetrahydro-bond lengths, 3, 621 synthesis, 3, 777... 

Pyrano[3,4-i]indol-3-one (329) enters the Diels-Alder reaetion with methoxy-butenone as an eleetron-rieh olefin [92JCS(P1)415]. After deearboxylation of the primary adduet330,2-aeetyl-3-methoxy-l, 9-dimethyl-2,3-dihydroearbazole (331) eliminates methanol to form 2-aeetyl-l,9-dimethylearbazole (332) [92JCS (Pl)415]. 

Pyrano-[4,2-b]-pyrrol-5-ones (40) and pyrano-[4,3-b]-pyrrol-6-ones (41) (Figure 2.4) are stable cyclic analogs of pyrrole 2,3-quinodimethane and undergo Diels Alder reaction [40, 41] with various dienophiles to afford indole derivatives after loss of carbon dioxide. 

Both ( )-l-phenylsulfonyl and (5)-(+)-3-p-tolylsulfmyl -alk-3-en-2-ones can exhibit high diastereoselectivity in their reactions with vinyl ethers and styrenes, with the dienophile having a dominant influence on the stereochemical outcome <96T1205,96TL3687>. Indol-2-ylideneacetic acid esters can act as both dienophile and heterodiene in cycloaddition reactions in the latter case pyrano[3,2-h]indoles are formed <96SYN519>. 

Litvinov YM, Shestopalov AA, Rodinovskaya LA, Shestopalov AM (2009) New convenient four-component synthesis of 6-amino-2,4-dihydropyrano 2,3-c pyrazol-5-carbonitriles and one-pot synthesis of 6 -aminospiro (3H)-indol-3,4 -pyrano 2,3-c pyrazol -(lH)-2-on-5 -carbonitriles. J Comb Chem 11 914—919... 

Moody et al. reported the sjmthesis of the 3-oxygenated carbazoie alkaloids, hyellazole (245) (591,592) and carazostatin (247) (593,594) based on their pyrano[3,4- 7]indol-3-one methodology (Scheme 5.57). This synthetic strategy involves the use of a 1-substituted pyrano[3,4- 7]indol-3-one 542 as a stable... 

Moody and Rahimtoola reported a short synthesis of staurosporinone (293) without the use of protecting groups at the indole or the lactam nitrogen (761,762). This route involves an intramolecular Diels-Alder reaction of the pyrano[4,3- 7]indol-3-one 1325 and a subsequent cyclization by nitrene insertion. The pyrano[4,3-l7]indol-3-one 1325 was obtained in four steps from ethyl indol-2-yl... 

To a suspension of 500 mg (1.74 mmoles) of the (S)-6-(2-oxo-l,3-oxazolidin-4-ylmethyl)-4,9-dihydro-3-pyrano-[3,4-b]indol-l-one in 10 ml of methanol were added 0.12 ml (1.9 mmoles) of methanesulfonic acid. The mixture was left under stirring at the reflux temperature for 3 hours. The solvent was evaporated to dryness under reduced pressure, the residue dissolved with 10 ml of a saturated bicarbonate solution and extracted three times with dichloromethane. The combined organic phases were dried and evaporated to dryness and the evaporated solid recrystallised from ethanol to give 517 mg (93%) of the title ester as a yellow crystalline solid. Melting point 178°-180°C. 

Several cyclopenta[b]indoles were prepared from cyclopenta[b]pyrano[3,4-d]pyrrol-6-one 52a. <95JCS(P1 )1131 >... 

Pyrano[2,3-g ben20xaax l-9-one, 1026 Pyranol 2,3-6 6.5-6 ]dipyridin-5-one, 823 Pyranoj 2,3-6 ]indol-4-mie, 808 Pyrano 3,4-6jindol-3-oae. 802 Pyranoi4,3-6jindol-3-one, 803 PyraBo 3, 2 5,6]pyrano 4,3-6 Jbenzopyran-... 

Cycloalka[o]carbazoles have been prepared by the IMDA reaction of l-(w-alkynyl)pyrano[3,4-h]indol-3-ones with subsequent cycloelimination of carbon dioxide30. 

Cycloaddition reactions continue to find application in the synthesis of natural products and related substances containing indole and carbazole rings. Moody has published a summary of syntheses of carbazole alkaloids in which cycloadditions of pyrano[3,4-b]indol-3-ones figure prominently. <94SL681>... 

Pyrano[3,4-i]indol-3-ones also react with alkenes having electron-donor substituents such as ethyl vinyl ether, vinyl acetate, dihydropyran and iV-vinylpyrrolidone. The oxygen substituents are eliminated to provide fully aromatized carbazoles. The amido substituent, on the other hand, is retained (Scheme 153) <92JCS(pi)415>. 

Pyrano[3,4- >]indole-3-ones serve as another alternative precursor to indolo-2,3-qui-nodimethane analogs and have been shown to readily participate in Diels-Alder cycloaddition reactions with a variety of electron-deficient dienophiles [112]. For reactions with electron-rich alkenes, however, heating in a sealed tube and very long reaction times (80-120°C, several days) were reported to be necessary [134, 135], thus reducing the usefulness of these reactions as a general synthetic approach. 

It is not surprising then that since the publication of the Pindur review [112], there have been a few additional reports highlighting the utility of pyrano[3,4-Z>] indole-3-ones as building blocks in Diels-Alder reactions, all using electron-deficient dienes. Haider et al. [136] investigated the cycloadditions of pyranoindolones... 

Van Broeck PI, Van Doren PE, et al (1992) Diels-Alder reactions of pyrano[3,4-b]indol-3-ones and a 2-benzopyran-3-one with hetero substituted olefins generation of carbazole and naphthalene derivatives by elimination instead of dehydrogenation. J Chem Soc, Perkin Trans 1 415 19... 

The first example of an indole-2,3-quinodimethane (IQM) undergoing a Diels-Alder cycloaddition to furnish a carbazole was reported by Plieninger and coworkers in 1964 [9], Thus, indole-3-acetic acid was readily converted to pyrano[3,4-fe]indol-3-ones upon treatment with carboxylic acid anhydrides (Scheme 1, equation 1). These stable synthetic equivalents of IQMs undergo Diels-Alder reactions with electron-deficient dienophiles (A-phenytma-leimide,maleicanhydride,dimethylacetylenedicarboxylate) (equation 2). Plieninger s discovery notwithstanding, it was Moody and coworkers who parlayed this chemistry into a powerful carbazole synthesis (equations 3,4) [10-18],... 

Moody and coworkers synthesized and explored the Diels-Alder chemistry of the isomeric pyrano[4,3-fe]indol-3-ones (Scheme 3, equations 1, 2) [19, 20]. The requisite... 

Scheme 2 Moody Carbazole Synthesis from Pyrano[3,4-b]indol-3-ones...

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