By Gordon W. Gribble and Thomas L. Gilchrist (Eds.)

This quantity of growth in Heterocyclic Chemistry (PHC) is the fourteenth annual evaluate of the literature, protecting the paintings released on vital heterocyclic ring platforms in the course of 2001. during this quantity there are really good reports. the 1st, through Jan Bergman and Tomasz Janosik, covers their paintings on sulfur-containing indoles. the second one, through David Knight, discusses five- endo -trig iodocyclisations. the next chapters, prepared via expanding heterocycle ring measurement, overview contemporary advances within the box of heterocyclic chemistry with emphasis on synthesis and reactions.

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No competing 5-endo products arising from cleavage of the MOMO function were observed. We have compared the relative facility of protecting group cleavage in both 5-exo and 5-endo modes under the same conditions (see above) <01MI001>. In the 5-exo examples [41 to 42], the presence of protecting groups hardly slowed the cyclization. This was also true of the corresponding 5-endo cyclizations [43 to 13] which generally took about twice as long to reach completion relative to the 5-exo reactions. Hence, the use of protecting groups to block an undesired pathway must be approached with caution in this area.

However, when a furan ring is conjugated to the alkene 181, then pyrrolidine formation 182 does ensue, presumably by a rather different 5-exo process, as argued above in respect of the Kang tetrahydrofuran synthesis 50. ~ P r HO NHTS TsHN I 178 III TsHN (~) /'~/" Pr HO" 180 OH 179 181 Ts " o r ~ 182 Pr As exemplified above, the inclusion of more substituents can often assist cyclization. A further example of this concerns iodocyclizations involving monosubstituted alkenes which were found to be rather poor during our model studies <01JCS(P1)l182>.

I. 113 " HOH~~ H . OR OH 114 Bicyclic systems can also be formed efficiently and highly stereoselectively using 5-endotrig iodocyclizations <00JCS(P1)3469>. In the light of the foregoing transition state conformations, we were not too surprised to find that both (E)- and (Z)-trans-2alkenylcyclohexan-l-ols 115 underwent smooth cyclization to give only the perhydrobenzofurans [116; n = 1]. Understandably, due to the strain associated with a transring fusion, the corresponding 5/5 systems were not formed with similar facility: the (Z)isomer failed completely but we were able to isolate a 29% yield of the product 117 from the (E)-trans-alkenylcyclopentanol [115; n - 0; E = Bu; Z = H].

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