2,3 -dichloro-4- -pyrrole

Rearrangement of A-haloazoles to C-haloazoles is a typical reaction of /V-haloazoles capable of halogenation at a ring-carbon atom. A -Chloro-pyrrole 1, while heated with methanol, gives a mixture of pyrrole (30%), 2-chloropyrrole (—30%), 3-chloropyrrole (15-20%), and 2,5-dichloro-pyrrole (—10%) (82JOC1008). On the addition of the basic resin Amberlist A-21 to the reaction mixture the formation of 2-chloro-, 3-chloro-, and 2,5-dichloropyrrole sharply decreases (to 0.5-3%) (Scheme 26). 

Pyridazinones may undergo ring contraction to pyrroles, pyrazoles and indoles, the process being induced either by an acid or base. The structure of the final product is strongly dependent on the reaction conditions. For example, 4,5-dichloro-l-phenylpyridazin-6(lFT)-one rearranges thermally to 4-chloro-l-phenylpyrazole-5-carboxylic acid (12S), while in aqueous base the corresponding 4-hydroxy acid (126) is formed (Scheme 40). 

Pyrrole, 1 -benzyl-2-(2-carboxybenzoyl)-intramolecular acylation, 4, 221 Pyrrole, l-benzyl-2,5-dichloro-3,4-diformyl-reactions... 

Pyrrole, 3,4-dialkyl-2-ethyl-5-methyl-benzoylation, 4, 220 Pyrrole, 1,2-diamino-reactions, 4, 300 Pyrrole, 2,5-diamino-tautomerism, 4, 200, 299 Pyrrole, 2,4-diaryl-nitration, 4, 210 Pyrrole, 2,5-diaryl-synthesis, 4, 343 Pyrrole, 3,4-diaryl-synthesis, 4, 343 Pyrrole, di-t-butyl-protonation, 4, 47 Pyrrole, 2,5-dichloro-synthesis, 4, 368... 

Bis(3,4-diethyl-2-pyrrolylmethyl)-3,4-dietliyl-l//-pyrrole (2), prepared in situ from the di-t-butylester of the 5,5 -dicarboxylic acid (/), reacts with 4//-1,2,4-triazole-3,5-dialdehyde (3) in di-chloromethane in the presence of trifluoroacetic acid and 2,3-dichloro-5,6-dicyano-/)-benzoquino-ne as an oxidation reagent. Dark blue crystals are obtained after chromatographic purification. The dark violet chloroform solution fluoresces purple at 360 nm and gives the NMR experiments 39. Which compound and which tautomer of it has been formed ... 

In some instances, the azaquadricyclane is nonisolable and photolysis of the pyrrole-dimethyl acetylenedicarboxylate cycloadduct or of analogous cycloadducts gives directly the 1 //-azepine. For example, 3.6-dichloro-l-tosyl-l//-azepine (10) is produced in excellent yield by photolysis of the [4 + 2] cycloadduct 9.22 Interestingly, dichloroazepine 10 is found (by H NMR spectroscopy) to be in equilibrium with a small amount (1 % at — 67 C) of its bicyclic valence tautomer 11. 

To probe interactions between active silanol sites and the isothiazolin-based biocides a number of model probes were investigated 12. The adsorbates (1-methylpyrro lidin-2-one, pyridine, pyrrolidine, pyrrole, 2-methylthiophene, 2-octyl-4-isothiazolin-3-one, 4,5-dichloro-2-octyl-4-isothiazolin-3-one and 2-cyclopenen-l -one,) varied in basicity, polarity and 7i-character. The amounts of the adsorbates retained by... 

The difference between the Fe-S bond lengths in the high spin and low spin states is about 0.15 A, which is also in line with the Fe-S bond lengths for the low spin tris(l-pyrrole-dithiocarbamato)iron(III) hemikis(dichloro-... 

Tetraphenylporphin (H2TPP) was prepared from pyrrole and benzaldehyde (25). The tetraphenylchlorin contamination was oxidized by use of 2,3-dichloro-5,6-dicyano-p-benzoquinone (26). Octaethylporphin (H2-OEP)was prepared by the method of Paine et al.(27) from 3,4-diethyl-2-ethoxy-carbony1-5-methyl-pyrrole (28). Zinc(II)-tetraphenylporphin (ZnTPP) was prepared by refluxing H2TPP and zinc acetate in dimethyl-formamide (29). ZnTPP was dissolved at a concentration of 10 -10 ... 

For the first time, application of sequential Diels-Alder reactions to an in situ-generated 2,3-dimethylenepyrrole was shown with various dienophiles 548 to afford 2,3,6,7-tetrasubstituted carbazoles (549). This novel tandem Diels-Alder reaction leads to carbazole derivatives in two steps, starting from pyrrole 547 and 2 equivalents of a dienophile, and is followed by 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) oxidation of the intermediate octahydrocarbazole. Mechanistically, the formation of the intermediate octahydrocarbazole appears to involve two sequential [4+2] cycloadditions between the exocyclic diene generated by the thermal elimination of acetic acid and a dienophile (529) (Scheme 5.17). 

The 4- and 6-positions of pyrrolo[2,3-3]pyridines can be substituted via palladium-catalyzed cross-coupling reactions with the 4- or 6-halo-substituted derivatives (Scheme 3) <2001SL609>. Nucleophilic displacement of the 4-substituent of 6-chloro-4-nitro- and 4,6-dichloro-pyrrolo[2,3-/ ]pyridines takes place with phenols. Protection of the pyrrole nitrogen with a /3-trimethylsilylethoxymethyl (SEM) group affords good yields of the aryl ethers (Equation 3) <2006TL2069>. 

Chlorination of THF is achieved with chlorine at low temperature and affords the 2-chloro and 2,5-dichloro compounds. The latter with primary amines gives TV-substituted pyrroles. Monochlorination is best achieved with sulfuryl chloride (Section 3.11.4.1), and the 2,3-dichloro compound is available by addition of chlorine to 2,3-dihydrofuran. This compound... 

The following chemicals were obtained from Aldrich Chemical Company, Inc. and used without further purification 1,3-dimethoxybenzene (99%) butyl lithium (1.6 M in hexanes) 1-formylpiperdine (99%) boron trifiuoride-diethyl ether (purified, redistilled) 2,3-dichloro-5,6-dicyano-l,4-benzo-quinone (98%), and pyridine hydrochloride (98%). All solvents were reagent grade and were obtained from Fisher Scientific and used without further purification except where noted. Silica gel (230-400 mesh) was obtained from EM Scientific. Chloroform was stored over activated, 4-A molecular sieves for at least 24 h prior to use. Tetrahydrofuran (optima grade) was distilled from sodium benzophenone. Pyrrole (99%) was obtained from Aldrich Chemical Company, Inc. and distilled from calcium hydride. 

Some details concerning the synthesis of pyrroles from ketoximes and 1,2-dichloro- or 1,2-dibromoethanes in the KOH/DMSO system are described in a patent (82MIP1). The reaction proceeds smoothly and at a fairly high rate at 90-120°C. It is recommended that ketoxime, 1,2-dihaloethane, and KOH be taken in a molar ratio of 1 (2-3) (7-10) and the process carried out at 100°C for 2.5-6 hr. The preferable ketoxime/ DMSO volume ratio is 1 10. 

Run Oxime 125 Oxime/dichloro-ethane/KOH ratioc, Temp. <°C) Reaction time (hr) Pyrrole 126 Yield (GLC) (%) N-Vinyl-pyrrole 127 Diether 128... 

American workers needed to prepare the bis-amino acid 1 and adopted a literature procedure in which two equivalents of diethyl acetamidomalonate were to be alkylated with one equivalent of l,4-dichloro-2-butyne using two equivalents of sodium ethoxide in hot ethanol. Hydrolysis and decarboxylation of the dialkylated malonate would then give 1. This alkylation reaction was carried out, but ten equivalents of sodium ethoxide were used rather than two. This resulted in formation of ethyl 5-methylpyrrole-2-carboxylate in ca. 40% yield. Further study showed that the reaction to produce the pyrrole required equimolar amounts of the acetamidomalonate and the dichlorobutyne, excess of sodium ethoxide, and heating. No pyrrole was formed at room temperature. 

X-Ray crystal structures are provided for several of the pentathiepins, for example, 6,8-dichloro-7-methyl-77/-[l,2,3,4,5]pentathiepino[6,7-f]pyrrole, 6,8-dichloro-7-/-butyl-777-[l,2,3,4,5]pentathiepino[6,7-c]pyrrole <2005OBC3496>, and bispiperidinothienopentathiepine <20030L1939>. In general, the geometry of this pen-tathiepines is quite close to other pentathiepines. 

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