Pyrroles 2.3- dihydro

The pyrrolines or dihydropyrroles can exist in three isomeric forms 1-pyrroline (3,4-dihyro-2JT-pyrrole [5724-81-2]) (16) is an unstable material that resiniftes upon exposure to air 2-pyrroline (2,3-dihydro-lJT-pyrrole [638-31-3]) (17) is even more unstable only 3-pyrroline (2,5-dihydro-lJT-pyrrole [109-96-6]) (18) is reasonably stable. 3-Pyrroline bods at 91°C and has a density of 0.9097 g/cm and a refractive index of 1.4664. 

Chemical antiozonants comprise the second general class of commercial antiozonants. Of the many compounds reported to be chemical antiozonants, nearly all contain nitrogen. Compound classes include derivatives of l,2-dihydro-2,2,4-trimethylquinoline, A/-substituted ureas or thioureas, substituted pyrroles, and nickel or zinc dithiocarbamate salts (see also Antioxidants). The most effective antiozonants, however, are derivatives of -phenylenediamine... 

Reduction of isoindoles with dissolving metals or catalytically occurs in the pyrrole ring. Reduction of indolizine with hydrogen and a platinum catalyst gives an octahydro derivative. With a palladium catalyst in neutral solution, reduction occurs in the pyridine ring but in the presence of acid, reduction occurs in the five-membered ring (Scheme 38). Reductive metallation of 1,3-diphenylisobenzofuran results in stereoselective formation of the cw-1,3-dihydro derivative (Scheme 39) (80JOC3982). 

H-Pyrrole, 3,4-dihydro-5-methyl-UV, 4, 179 (65JCS2313) lH-Pyrrole-3-acetic acid, ester C NMR, 4, 172 (74JCS(P2)1004)... 

Furan, 2,5-dialkoxy-2-( 1 -hydroxyalkyl)-2,5-dihydro-ring expansion, 1, 425 Furan, 2,5-dialkoxytetrahydro-pyrrole synthesis from, 4, 330 Furan, 2,4-dialkyl-synthesis, 4, 661, 685 Furan, 2,5-dialkyl-... 

Furo[2,3-amino-synthesis, 4, 986 Furo[3,4-d]pyrimidinedione synthesis, 4, 987 Furopyrimidines, 4, 986 Furo[2,3-d]pyrimidines synthesis, 4, 986 Furo[3,2-d]pyrimidines synthesis, 4, 987 Furo[3,2- 6]pyrone synthesis, 4, 994 Furo[3,2-c]pyrone synthesis, 4, 993 Furo[3,2-6]pyrrole, hexahydro-biological activity, 6, 1024 1 H-Furo[3,4-6]pyrrole-2,3-dione, 4,6a-diphenyl-6-(phenylimino)-6,6a-dihydro-synthesis, 6, 1004 Furopyrroles... 

Thieno[2,3-d ]pyrimidin-4(3 H) -one, 3-methyl-synthesis, 4, 1017 Thieno[2,3-d ]pyrimidin-4-ones synthesis, 4, 1017, 1018, 1022 Thieno[2,3-6]pyrrole, 5-aryl-synthesis, 6, 1009 Thieno[2,3-6]pyrrole, N-benzyl- H NMR, 4, 1042 UV spectra, 4, 1044 Thieno[2,3-c]pyrrole, N-ethyl-UV spectra, 4, 1044 Thieno[3,2-6]pyrrole, 5-aryl-synthesis, 6, 1009 Thieno[3,2-6]pyrrole, N-benzyl- H NMR, 4, 1041, 1042 lithiation, 4, 1051 UV spectra, 4, 1044 Thieno[3,2-6]pyrrole, 2,3-dihydro-desulfurization, 6, 984 oxidation, 6, 981... 

Thieno[3,2-6]pyrrole, 5-ethoxycarbonyl-acylation, 4, 1050 synthesis, 4, 1070 Thieno[3,4-c]pyrrole, 5,6-dihydro-synthesis, 6, 987... 

I) of which one form (picrate, m.p. 116°) is identical with dl-dihydro-de-N-methylheliotridane and the other (picrate, m.p. 126°) is diastereoisomeric with, and convertible into, it by, dehydrogenation to the corresponding pyrrole and hydrogenation of the latter in presence of copper chromite as catalyst. 

The importance of ring size holds also for tautomerism of -pyrrol-5-ones and. d -dihydro-6-pyridones. While the former compounds behave as cyclic 1-methyl-2-alkyl-2-hydroxy-5-pyrrolidones 179) (76) [or, on distillation, as the dehydrated l-methyl-2-alkyl-J -pyrrolones (77)], the latter compounds exist as acyclic N-methylamides of 8-oxo-acids (78) [as shown by infrared spectroscopy (/80)j. The dehydration of 78 during distillation to form l-methyl-2-alkyl-. -dihydro-6-pyridones (79) is achieved only with difficulty. 

A useful and possibly more general alternative to the Lwowski synthesis- of 1,3-diphenylisoindoles involves condensation of a l,2-dibenzoyl-l,4-cyclohexadiene (e.g., 55) with ammonia or a primary amine. Cyclohexadiene derivatives of this type are easily prepared by Riels-Alder addition of a 1,3-diene to dibenzoylacetylene, and these adducts lead directly, and in high yield, to the corresponding isoindoles (56). The reaction is closely related to the well-known synthesis of pyrroles by condensation of 1,4-diketones with ammonia. 4,7-Dihydro- and 4,5,6,7-tetrahydroisoindoles (57 and 58) have been... 

The rearrangement of cyclic sulfoxide 130a, which could be obtained from the corresponding thiolsulfinate 163 (Section III.C.l), was studied in different experimental conditions. The ci3-sulfoxide refluxed in toluene for 24 h gave a 1 1 mixture of the pyrrole 131 and the dihydro-1,4-thiazine 132. 

Methyl-3-(10,11-dihydro-5H-dibenzo[a,d]cycloheptene-5-ylidene)-1 -pyrrol ine Ethyl iodide Sodium borohydride... 

Irradiation of 4-methyl-5,7-diphenyl-3//-l,2-diazepine at — 70°C gives 5-methyl-l,6-diphenyl-4,6a-dihydro[l,2]diazeto[l,4-a]pyrrole in 83% yield.105... 

Chlorophyll a, the green photosynthesis pigment, is the prototype of the chlorin (2,3-dihydro-porphyrin) class of products. It was first isolated by Willstatter1 at the turn of the century. The common structural unit in this class is the chlorin framework named after chlorophyll. The chromophore with a partially saturated pyrrole ring, which is formally derived from the completely unsaturated porphyrin, is less symmetric than the latter and systematically named according to IUPAC nomenclature as 2,3-dihydroporphyrin. 

The pyrrolotriazines 32 were prepared from 3,4-dihydro-5-ethoxy-2//-pyrrole 31 by sequential reaction with hydrazine hydrate and a-oxoesters (85GEP3340026). They are useful as selective herbicides (Scheme 10). 

Even in Ugi reactions of chiral 4,5-dihydro-3//-pyrrole derivatives with aryloxy substituents vicinal to the cWo-cyclic imino group, a low stereoselectivity was found with either chiral or achiral isocyanides and benzoic acid leading to substituted 2-aminoearbonyl-3-aryl-oxy-1 -benzoylpyrrolid ine derivatives82. 

Propionic acid, 2-iodo-3-nitro-, ethyl ester [Propanoic acid, 2-iodo-3-mtro-, ethyl ester], 65 2//-Pyran, 3,4-dihydro-, 51 2//-PYR AN-2-ONE, 49 2H Pyran 2-one, 5 bromo 5,6-dihydro, 50 27/-PYRAN-2-ONE, 5,6 DIHYDRO-, 49 PYRIDINE, 2,3,4,5 TETRAHYDRO, 118 Pyridines, -substituted, 34 a Pyrone-6-carboxyhc acid [2H Pyran-6-Larboxyhc acid 2-oxo ], 51 Pyrroles, 34... 

The primary fragmentations of 5-methylsulfonyl-6-phenyl-2-pyridone (41) and its 3,4-dihydro analogue (42) are dominated by the methylsulfonyl substituent and not by the pyridone moiety26. Equation (18) summarizes the most important primary fragmentations and shows that the pyridone ions m/z 186 and 170 yield the pyrrole-type ions m/z 158 and 142 only after the sulfonyl side-chain has been broken off. Since the mass spectrum... 

Isonitriles react with alkenylcarbene complexes to form initially at 0 °C a 3-ethoxy-3-styrylketeneimine complex, which on warming to room temperature leads to the formation of a cyclic 3-ethoxy-2,5-dihydro-2-pyrrolylidene complex. Finally, on heating to 100 °C a pyrrole derivative is produced [80] (Scheme 33). 

Die Reduktion cyclischer Schiff scher Basen mit Hydriden verlauft ahnlich den acycli-schen Verbindungen zu Aminen. Azirine werden durch Lithiumalanat zu den Aziridi-nen reduziert, mit Natriumboranat in Methanol erfolgt dagegen Solvolyse zum Me-thyl-aminomethyl-ather5. 4,5-Dihydro-3H-pyrrol-Derivate lassen sich mit Lithiumalanat6 und Natriumboranat7 zu Pyrrolidinen reduzieren. Ahnlich konnen auch Pipe-... 

Benzenediamine (538) and l-diphenylamino-3,4-dihydro-[l]benzothiopy-rano[4,3-/ ]pyrrole-2,3(l//)-dione (539) in dichloromethane (containing a trace of hydrogen chloride) at 20°C for 48 h furnished 3-(4-diphenylhydrazono-3,4-dihydro-2//-[l]benzothiopyran-3-yl)-2(l//)-quinoxalinone (540) in 30% yield. 

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