5-endo-dig Cyclisations of homopropargylic sulfonamides: a new route to 2,3-dihydropyrroles and β-iodopyrroles

Synthesis of aromatic heterocycles

“…56 Knight and co-workers have adapted their iodocyclisation reactions to provide routes 2,5-disubstituted pyrroles with or without an iodo substituent at C-3. 57, 58 The methodology is illustrated in Scheme 20. 58 The synthesis of methyl 2-arylpyrrole-3-carboxylates from methyl buta-2,3-dienoate which is exemplified in Scheme 21 is conceptually quite different but probably involves the same kind of endo-cyclisation and aromatisation steps.…”

“…57, 58 The methodology is illustrated in Scheme 20. 58 The synthesis of methyl 2-arylpyrrole-3-carboxylates from methyl buta-2,3-dienoate which is exemplified in Scheme 21 is conceptually quite different but probably involves the same kind of endo-cyclisation and aromatisation steps. 59 Other new cyclisation reactions in which the N-C2 bonds of pyrroles are formed are illustrated in Scheme 22 60 and Scheme 23.…”

Synthesis of 2(3H)-Furanones via Electrophilic Cyclization

“…The electrophilic cyclization of functionally-substituted alkynes has attracted much attention due to its wide utility in the preparation of a range of useful, functionally-substituted heterocycles and carbocycles, 5 such as quinolines, 6 isoxazoles, 7 isoindolin-1-ones, 8 benzo[b]thiophenes, 9 bicyclic β-lactams, 10 indoles, 11 chromones, 12 isochromenes, 13 2-naphthols, 14 benzofurans, 15 cyclic carbonates, 16 pyrroles, 17 furans 18 isocoumarins, 19 α-pyrones, 19 isoquinolines, 20 naphthyridines, 20 polycyclic aromatics, 21 naphthalenes, 22 and furopyridines. 23 Herein, we report an efficient approach to various highly substituted 2(3H)-furanones by the electrophilic cyclization of 3-alkynoate esters and acids.…”

Five‐Membered Heterocycles: Pyrrole and Related Systems

“…Annulation of the homopropargylic sulfonamides 48 (R¼Ph, 2-furyl, 2-thienyl), which are prepared by alkylation of the benzophenone imine of methyl glycinate with propargyl bromide, followed by sequential hydrolysis, tosylation and Sonogashira coupling at the terminal acetylene unit, has been reported to give the substituted 4-iodo-2,3-dihydropyrrole derivatives 49 via a 5-endo-dig process, eventually leading to the b-iodopyrroles 50 (Scheme 4.17) [103,104], whereas cyclization of related alkenyl derivatives provides access to b-iodopyrrolidine derivatives [105].…”