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Overall 5-endo cyclisations of the C-allylic glycine sulfonamides 5 lead to usually excellent yields of the 2,5-cis-or 2,5-trans-pyrrolidine-2-carboxylates 11 and 12 respectively, depending upon whether base is absent or present. While reductions to the corresponding pyrrolidine-2-methanols 13 proved efficient, subsequent eliminations of the elements of hydrogen iodide gave mixtures of products 14-16. Suitably positioned hydroxy groups compete successfully with the sulfonamide via a 5-exo cyclisation mode. However, when such a substrate contains a furan ring attached to the alkene function ( 21), then cyclisation does occur at the sulfonamide, presumably by participation of the furan oxygen, to give an iodopyrrolidine-2-methanol 13a. Finally, base-induced elimination of both hydrogen iodide and toluene-psulfinic acid from the initial iodopyrrolidines 11 and 12 leads to 5-substituted pyrrole-2-carboxylates 26. Overall, this sequence is complementary to the Kenner pyrrole synthesis.Electrophile-induced 5-endo-trig cyclisations are now well established as a viable and often highly stereoselective approach to tetrahydrofurans. 1-5 In line with these studies, we have shown that similar cyclisations of the (E )-homoallylic sulfonamides 1 by treatment with excess iodine in the presence of anhydrous potassium carbonate lead smoothly to the 2,5-trans-iodopyrrolidines 2, most likely via the chair-like transition state 4. An unexpected bonus was the discovery that if the same sulfonamides 1 were cyclised solely in the presence of iodine, then the corresponding 2,5-cis-isomers 3 were the only products formed (Scheme 1

Iodocyclisations of the allylic glycinates 7 lead either to the trans-or cis-2,5-disubstituted proline derivatives 8 or 9, depending on the reaction conditions; subsequent treatment of these with DBU in DMF gives the 2-pyrrolecarboxylates 10 and 13 in excellent yields by a double elimination of hydrogen iodide and toluenesulfinic acid.Electrophile-induced cyclisations of unsaturated alcohols and amine derivatives have been widely used for the synthesis of both five-and six-membered saturated heterocycles, typically by 5-or 6-exo processes. 1 In a continuation of our studies of the less common, electrophile-induced, 5-endo-trig cyclisations, 2 we have reported that, when applied to (E)-homoallylic tosylamides 1, these reactions provide a useful, stereodivergent route to either trans-or cis-2,5-disubstituted-3-iodopyrrolidines [2 and 3 respectively], depending upon the conditions employed (Scheme 1). 3 Thus, under basic conditions, the 2,5-trans isomers 2 are obtained, typically in a ratio of ≥15:1, with the minor isomer having the corresponding 2,5-cis stereochemistry 3. In contrast, when the cyclisations are carried out in the absence of base, the latter isomers 3 are the sole products. It would appear that the trans-isomers 2 are the initial kinetic products which, under the acidic conditions [ii] resulting from hydrogen iodide release during the cyclisation, revert to the more thermodynamically stable isomers 3. Evidence for this is that the trans-isomers 2, after isolation, can be smoothly and rapidly converted into the corresponding cis-isomers 3 by exposure to iodine and hydrogen iodide in acetonitrile. 3 Scheme 1In this initial work, we only exemplified the cyclisations using relatively unfunctionalized substrates 1, wherein the substituents were either nalkyl or phenyl groups. In order to expand the synthetic potential of this methodology, it was therefore necessary to investigate whether other, potentially more reactive, functional groups were compatible with the cyclisation conditions. The danger in this is that incorporation of such functionality will inevitably introduce heteroatoms or unsaturation which could compete with the 5-endo process by more favoured 5-or 6-exo-trig pathways. In this respect, a methoxycarbonyl group seemed a likely candidate as this has been found not to participate readily in such cyclisations in general 2 and, if successfully incorporated, would result in the formation of a range of substituted prolines, as well as providing additional opportunities for subsequent homologation. Herein, we report the successful outcome of our initial work in this area, which has also resulted in the realization of a new pyrrole synthesis.The starting alkenyl glycines 7 were prepared by palladium(0)-catalysed coupling of the allylic carbonates 4 and the benzophenone imine of methyl glycinate 5 (Scheme 2). 4 We chose to exemplify the method using a phenyl, a 2-furyl and an alkyl substituent. The initial products 6 were isolated in 55-75% yields, following separation of the small amounts of regio...

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