Pyrroles 3-methyl

FIGURE 10.13 Pyrogram of the exoskeleton of a saltwater shrimp pyrolyzed at 750°C. Peaks 1 = acetic acid, 2 = pyrrole, 3 = methyl pyrrole, 4 = acetamide, 5 = 2,5-dimethylpyirole. 

Potential-Programmed Electropolymerization (PPEP). This technique allows compositional modulation over distances of the order of 100 A. Mesoscopic layered structures with high lateral quality are produced by the PPEP method. An improvement of the flatness and uniformity of the layered structure is achieved by careful choice of an appropriate working electrode (silicon single-crystal wafer), monomer (pyrrole/bithiophene or pyrrole/3-methyl-thiophene) and solvent (propylene carbonate). The PPEP method can produce materials having desirable properties tailored by the quantum size effect [703-705]. 

Unsymmetrically substituted dipyrromethanes are obtained from n-unsubstitued pyrroles and fl(-(bromomethyl)pyiToIes in hot acetic acid within a few minutes. These reaction conditions are relatively mild and the o-unsubstituted pyrrole may even bear an electron withdrawing carboxylic ester function. It is still sufficiently nucleophilic to substitute bromine or acetoxy groups on an a-pyrrolic methyl group. Hetero atoms in this position are extremely reactive leaving groups since the a-pyrrolylmethenium( = azafulvenium ) cation formed as an intermediate is highly resonance-stabilized. 

A new photoreaction is described for the tricyclic triazoline shown in Scheme 44, which upon irradiation in methanol gives a pyrrole methyl ester205 by retro Diels-Alder reaction of an intramolecular pyrrole-ketene Diels-Alder adduct (88) formed from the diradical (Scheme 154).205 In benzene, ketene dimerization occurs. 

The chemical shift of the A-pyrroline methyl group in the cyclazine (17) was diagnostic, occurring at 51.67 instead of in the 52.2-2.6 range observed for pyrrole methyl groups... 

A good starting point for parameter refinement of large molecules are values optimized on small fragments. In the case of bacteriochlorophylls, we started modeling their chemical constituents such as pyrrol, methyl acetate and methylic groups, for which DFT calculations were also made. Sub-... 

Ethanone, 1-(1H-pyrroi-2-yl)- (2-acety[pyrrole methyl 2-pyrrolyt ketone) 172a 174a, 174b... 

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]. 

Ethyl-4-methyl-l-(phenylsulfonyl)indole 4-Ethyl-7-methyl-l-phenylsulfonyl-l,5-dihydropyrano-[3,4-b]pyrrol-5-one phenyl vinyl sulfoxide 60 [3]... 

Methoxycarbonyl)-7-methyl-l-(phenylsulfonyl)- 5-trimethylsilylindole 7-Methyl-l-phenylsulfonyi-l,5-dihydropyrano[3,4-b]pyrrol-5-one ethyl 3-trimethyIsilyIpropynoate 53 [1]... 

Aldehydes and Ketones. Pyrrole aldehydes and ketones are somewhat less reactive than the corresponding benzenoid derivatives. The aldehydes do not undergo Cannizzaro or Perkin reactions but condense with a variety of compounds that contain active methylene groups. They also react with pyrroles under acidic conditions to form dipyrryhnethenes (26). The aldehydes can be reduced to the methyl or carbinol stmctures. The ketones undergo normal carbonyl reactions. 

Mercapto derivatives of furan, thiophene, selenophene (77ACS(B)198) and pyrrole (72AJC985) all exist predominantly in the thiol form. 2-Mercaptobenzothiophene is also a thiol (70JCS(C)243i) whereas 2-mercaptoindole is mainly indoline-2-thione (89) (69CPB550). The finely balanced nature of this system is indicated by the fact that a 3-aryl, but not a 3-alkyl, substituent will stabilize the 2-thiol form, whereas for 3-aryl-fV-methyl derivatives the 2-thione tautomer is preferred (71CC836). 

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