Pyrrole, 2,5-dimethyl

K.32) l//-Pyrrole, 2,5-dimethyl-l-(2-methylpropyl)-, I-isobutyl-2,5-dimethy/pyrrole, 2,5-dimethyl-]-(2-methylpropyl)pyrrole [21407-84-1]... 

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. 

SAFETY PROFILE Poison by inhalation and ingestion. A corrosive eye, skin, and mucous membrane irritant. Potentially explosive reaction with water evolves hydrogen chloride and phosphine, which then ignites. Explosive reaction with 2,6-dimethylpyridine N-oxide, dimethyl sulfoxide, ferrocene-1,1 -dicarboxylic acid, pyridine N-oxide (above 60°C), sodium -L heat. Violent reaction or ignition with BI3, carbon disulfide, 2,5-dimethyl pyrrole + dimethyl formamide, organic matter, zinc powder. Reacts with water or steam to produce heat and toxic and corrosive fumes. Incompatible with carbon disulfide, N,N-dimethyl-formamide, 2,5-dimethylpyrrole, 2,6-dimethylpyridine N-oxide, dimethylsulfoxide, ferrocene-1,1-dicarboxylic acid, water, zinc. When heated to decomposition it emits highly toxic fumes of Cl" and POx. 

Boger DL, Panek JS et al (1992) Preparation and Diels-Alder reaction of a reactive, electron-deficient heterocyclic azadiene dimethyl 1,2,4,5-tetrazine-3,6-dicarboxylate. 1,2-Diazine (dimethyl 4-phenyl-l, 2-diazine-3, 6-dicarboxylate) and pyrrole (dimethyl 3-phenylpyrrole-2, 5-dicarboxylate) introduction. Organic Synth 70 335... 

The preparation of 2 4-dimethyl-3 5-dicarbethoxypyrrole (II) is an example of the Knorr synthesis of pyrrole derivatives, involving the reaction of an -aminoketone (or a derivative thereof) with a reactive methylene ketone (or a derivative thereof). The stages In the present synthesis from ethyl acetoacetate (I) may be represented as follows ... 

As illustrated in Scheme 8.1, both 2-vinylpyrroles and 3-vinylpyiroles are potential precursors of 4,5,6,7-tetrahydroindolcs via Diels-Alder cyclizations. Vinylpyrroles are relatively reactive dienes. However, they are also rather sensitive compounds and this has tended to restrict their synthetic application. While l-methyl-2-vinylpyrrole gives a good yield of an indole with dimethyl acetylenedicarboxylate, ot-substitiients on the vinyl group result in direct electrophilic attack at C5 of the pyrrole ring. This has been attributed to the stenc restriction on access to the necessary cisoid conformation of the 2-vinyl substituent[l]. 

Pyrrole oxidizes in air to red or black pigments of uncertain composition. More usehil is the preparation of 2-oxo-A -pyrrolines, which is best carried out by oxidation of the appropriate pyrrole with in pyridine (37), eg, 3,5-dimethyl-ethyl-3-pyrrolin-2-one [4030-24-4] from... 

Vinyl Pyrroles. Relatively new synthetic routes based on a one-pot reaction between ketoximes and acetjiene ia an alkaU metal hydroxide—dimethyl sulfoxide (DMSO) system have made vinyl pyrroles accessible. It requires no pyrrole precursors and uses cheap and readily available ketones (42). 

Vinyl chloride reacts with sulfides, thiols, alcohols, and oximes in basic media. Reaction with hydrated sodium sulfide [1313-82-2] in a mixture of dimethyl sulfoxide [67-68-5] (DMSO) and potassium hydroxide [1310-58-3], KOH, yields divinyl sulfide [627-51-0] and sulfur-containing heterocycles (27). Various vinyl sulfides can be obtained by reacting vinyl chloride with thiols in the presence of base (28). Vinyl ethers are produced in similar fashion, from the reaction of vinyl chloride with alcohols in the presence of a strong base (29,30). A variety of pyrroles and indoles have also been prepared by reacting vinyl chloride with different ketoximes or oximes in a mixture of DMSO and KOH (31). 

Although it has not been possible to study the protonation of isoindole itself, it is clear that isoindoles are more basic than indoles or pyrroles. For example, 2,5-dimethyl-1,3-diphenylisoindole (40) has a p/sTa of 4-2.05 protonation of isoindoles occurs at positions 1 or 3. The pK for protonation of indolizine (10) at position 3 is 4-3.94 and that for carbazole (41) for protonation on nitrogen is estimated at -6.0. 

The reactions of pyrroles with dimethyl acetylenedicarboxylate (DMAD) have been extensively investigated. In the presence of a proton donor the Michael adducts (125) and (126) are formed. However, under aprotic conditions the reversible formation of the 1 1 Diels-Alder adduct (127) is an important reaction. In the case of the adduct from 1-methylpyrrole, reaction with a further molecule of DMAD can occur to give a dihydroindole (Scheme 48) (82H(19)1915). 

In order to exploit the reactions of the C-lithio derivatives of iV-unsubstituted pyrroles and indoles, protecting groups such as t-butoxycarbonyl, benzenesulfonyl and dimethyl-amino have been used 81JOC157). This is illustrated by the scheme for preparing C-acylated pyrroles (211) (8UOC3760). 

The oxidative coupling of 3,4-dimethyl-or 3,4-diphenyl-isoxazolin-5-one by activated Mn02 produced a 4,4 -bis(isoxazolinone) (519) and 2,4 -bis(isoxazolinone) (520). Hydrogenation of (519) over Pt02/H0Ac produced a pyrrole derivative while similar reaction of (520) produced an isomeric pyrrole (80JHC763). These reactions are shown in Scheme 152. 

H-Pyrrole-2-carboxamide, JV,JV-dimethyl-AG 4, 34 (76JOC3591, 77T1337), 194 (76JOC3591)... 

X-ray, 4, 160 (79AX(B)2228> lH-Pyrrole-2,4-diamine, 1-t-butyl-JV, JV -dimethyl-3-phenyl-JV -phenylsulfonyl-X-ray, 4, 160 (78BSB893) lH-Pyrrole-3-methanol, 4-acetyl-X-ray, 4, 160 (78AX(B)1248> lH-Pyrrole-3-methanol, 4-acetyl-, hydrate X-ray, 4, 160 (78AX(B)1248> lH-Pyrrole-3-propanoic acid, ester C NMR, 4, 172 (74JCS(P2)1004>... 

Pyrrole, 3-acetyl-l,2-dimethyl-4-nitro-5-(2-nitrophenyl)-reduetion, 4, 244... 

Pyrrole-2-carboxamide, N,N-dimethyl-conformation, 4, 194 Pyrrole-3-carboxamide, N,N-dimethyl-conformation, 4, 194 Pyrrolecarboxamides synthesis, 4, 242 Pyrrole-2-carboxamides synthesis, 4, 148, 360 Pyrrolecarboxylhydrazides Curtius degradation, 4, 362 Pyrrole-2-carboxylic acid, l-benzyl-3-hydroxy-ethyl ester... 

Pyrrole-2-carboxylic acid, 4,5-dimethyl-ethyl ester formylation, 4, 217 Pyrrole-2-carboxylic acid, 3-hydroxy-... 

Pyrrole-3-carboxylic acid, l-benzoyl-5-bromo-2,4-dimethyl-ethyl ester chlorination, 4, 271... 

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