4-Iodo-2,3-dihydropyrroles

An interesting approach to 2,5-disubstituted 4-iodo-2,3-dihydropyrroles (8) has been reported, based on the cyclization of the sulfonamides 9 with iodine in the presence of potassium carbonate. The products could be dehydrogenated in good yields giving the corresponding pyrroles 10 with 2 equiv. of DBU at room temperature, while the use of only one equiv. of the base at elevated temperature led to partial loss of the iodine atom . 

Heterocyclization. Formation of A-tosyl-2-iodomethylaziridine from A-tosyl-allylamine requires iodine and NaH, whereas Ij-LiAl(OBu ) mediates cyclization of allyl A-acylcarbamates." A route to 4-iodo-2,3-dihydropyrroles by iodine-induced cyclization of homopropargylic sulfonamides involves a 5-endo-dig cyclization. ... 

When three molar equivalents of AgOAc were added to a previous protocol for the synthesis of a 4-iodo-2,3-dihydropyrrole derivative, the yield increased from 30% to 83%. In general, the addition of AgOAc gave reasonable yields (69-87%) for the synthesis of 4-iodo-2,3-dihydropyrroles from homopropargylic sulfonamides via a 5-endo-dig cyclization (eq 25). ... 

A similar intermolecular cyclization was recently utilized in the synthesis of highly substituted dihydropyrrole derivatives [133 -135]. In a specific example, the addition of pentadienyltosylamide derivatives 177 to propynyl(phenyl)iodo-nium triflate initiates a sequence of transformations that furnishes the complex, highly functionalized cyclopentene-annelated dihydropyrrole products 178 in moderate yields with complete stereoselection (Scheme 66). Under similar reaction conditions, the isomeric isoprene-derived tosylamide 179 reacts with propynyl(phenyl)iodonium triflate to give azabicyclo[3.1.0]hexane 180 as the final product [134]. 

Syntheses from Non-Carbohydrate Sources. The Birch reduction of an iV-protected 2-carboxymethyl substituted pyrrole and subsequent quench with an appropriate electrophile e.g. methyl 2,3,4-tri-0-benzyl-6-deoxy-6-iodo-a-D-glucopyranoside) affords a simple route to N-protected 2,2-disubstituted dihydropyrroles 81. These can be further elaborated into the corresponding 4-sub-stituted imino-ribitols 82 in good overall yield by a simple strategy of reduction, acetylation, syn-dihydroxylation and deprotection. ... 

Lautens et al. [344] reported the termination of a cascade of two intramolecular Heck 5-exo-trig carbopalladations by iodide leading from the o-bromobenzamide derivative 159 in the presence of potassium iodide to the heterotricycle 160 in 88% yield (Scheme 8.39). The same transformation was observed for the o-iodo analog of 159 and other o-iodophenyl derivatives with alkenyl side chains leading to various benzannelated dihydrofuran and dihydropyrrole derivatives. 

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