3- Iodo pyrroles

Iodo Pyrroles by a Consecutive 3CR of Acid Chlorides, Propargyl Amides, and Iodide... 

Scheme 39 Coupling-addition-cyclocondensation three-component synthesis of 4-iodo pyrroles 68...

The synthesized A-Boc-protected 4-iodo pyrroles 68 are highly useful synthetic building blocks, and the first scouting experiments were performed in the sense of a sequential Pd/Cu-catalyzed process [31], assuming that the catalyst system is stiU active after the coupling-addition-cyclocondensation sequence. Therefore, just upon addition of another terminal alkyne 4 to the reaction mixture, A-Boc-2-aryl-4-alkynyl pyrroles 69 can be obtained in good yields (Scheme 40) [201]. The conditions are sufficiently mild to leave the Boc group uncleaved. 

Since JV-Boc-protected 4-iodo pyrroles 38 are highly useful synthetic building blocks that can be transformed in the sense of a sequential Pd/Cu-catalyzed process, assuming that the catalyst system is still active after the coupling-addition-cyclocondensation sequence. Upon addition of another... 

Bruce A. Amdtsen of McGill University developed Organic Lett. 2009, 77, 1369) an approach to pyrroles such as 9, by condensation of an a,P-unsaturated a-cyano imine 7 with the acid chloride 8. Thomas J. J. Muller of Heinrich-Heine-Universitat Dusseldorf observed Organic Lett. 2009, 77, 2269) the condensation of an acid chloride 11 with a propargyl amine 10, leading to the iodo pyrrole 12. 

Pyrrole, 3-hydroxy-geometry, 4, 158 synthesis, 4, 343 tautomerism, 4, 36, 198 Pyrrole, 3-([Pg.816]

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... 

Methyl-l,2,3,9-tetrahydro-4H-carbazol-4-one, the key building block of the neuroactive compound alosetron, was easily obtained from 3-[(2-halophenyl)(methyl)amino]cyclohex-2-en-l-one by pyrrole ring formation via Heck reaction under microwave irradiation [94], While the iodo substrate gave an excellent yield in only 30 min at 100 °C the corresponding bromo derivative converted only poorly under the same reaction conditions (Scheme 88). 

In another example of a radical process at the pyrrole C-2 position, it has been reported that reductive radical cycloaddition of l-(2-iodoethyl)pyrrole and activated olefins, or l-(oj-iodo-alkyl)pyrroles 34 lead to cycloalkano[a]pyrroles 35 via electroreduction of the iodides using a nickel(II) complex as an electron transfer catalyst <96CPB2020>. Thus, it appears the radical chemistry of pyrroles portends to be a fertile area of research in the immediate or near future. 

An interesting approach to the pyrrolizidine skeleton was devised wherein pyrrole-2-carboxaldehyde (70) underwent A-allylation under basic conditions and subsequent olefmation with ethyl p-tolylsulfinylmethanephosphonate to produce the pyrrolyl alkene 71 <00TL1983>. Intramolecular Heck reaction of the iodo species then produced the 1 -p-tolylsulfinyl-1,3-diene 72. 

Various iodinated pyiToles have been prepared by direct iodination [19,24] or via thallation [25]. For example, 3-iodo-V-TIPS-pyrrole is prepared in 61% yield from 6 [19], and 3,4-diiodo-2-formyl-l-methylpyrrole is available in 54% yield via a bis-thallation reaction [25]. 

Iodocyclization of the olefinic tetrazole 5-but-3-enyl-l//-tetrazole 79 using Nal ICO ( and I2 in anhydrous acetonitrile at 0 °C under argon atmosphere in the dark affords a 72% isolated yield of a 1 1 mixture of 5-iodomethyl-6,7-dihydro-tetrazolo[l,5-zr] pyrrole 80 and 6-iodo-5,6,7,8-tctrahydro-tetrazolo[1,5-tf]pyridinc 81 (Equation 5) <2003T6759>. 

The I/Mg-exchange reaction can be extended to the use of iodo-substituted pyridines uracils , purines" , imidazoles , quinolines, imidazo[l,2-a]-pyridines, pyrroles ... 

The palladium catalysed annulation of / -iodoamines and acetylene derivatives has been widely used in the construction of pyrroles and indole derivatives. The strategy, first reported by Larock, is efficient in converting both cyclic and open chain 2-iodo-allylamine derivatives to 3-alkylidene-... 

The participation of halopyrroles in Heck coupling is mostly limited to intramolecular transformations. In a recent example of intermolecular Heck reaction different A-protcctcd 3-iodo-4-trimethylsilyl-pyrroles were coupled... 

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