7//-Pyrano indoles

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... 

HydroxycarbazoIes react with citral to form either pyrano[3,2-a]carbazoles (132) or pyrano[2,3]carbazoles (133), whilst 1-hydroxycarbazoles produce pyrano[2,3-a]-carbazoles (81SC823, 81H(16)1445). Other cyclization reactions involving substituted pyrroles or indoles and aldehydes or ketones in which the substituent becomes part of the new ring system are discussed under the relevant sections relating to the reactivity of the substituent. 

The pyrano[2,3-6]indoles 284 reacted with DMAD to give the carba-zoles 285, which have anti-inflammatory activity if R = H or lower alkyl. 181... 

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. 

The space group of the racemic compound was found to be Pbca, with cell constants of a = 8.60 A, b = 18.59 A, and c = 19.06 A. The stereoview of ( )-etodolac indicates that the oxygen of the pyrano ring and the acetic acid chain lie above the plane of the indole ring, and that the torsion angle aboiit the acetic acid side chain is 297.6°. The carbon atom of the carboxyl group is situated at 5.53 A from the center of the benzene ring, and lies in... 

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

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