%0 Journal Article %J Tetrahedron %D 2009 %T Influence of electronic factors on pd-mediated cycloisomerization: a systematic investigation of competitive 6-exo-dig versus 7-endo-dig cyclizations of sugar alkynols %A Ramana, C. V. %A Induvadana, Boddeti %A Srinivas, Burgula %A Yadagiri, Kommagalla %A Deshmukh, Madhusudhan N. %A Gonnade, Rajesh G. %K Alkynol cycloisomerization %K Bridged bicyclic ketal %K Palladium %K Sonogashira coupling %K Sugar alkynol %X

Pd-mediated cycloisomerization of 3-C-propargyl-ribo- and allofuranose derivatives was investigated in detail to understand the influence of electronic factors on the regioselectivity (6-exo- vs 7-endo) of alkynol cycloisomerization leading either to a six- or seven-membered ring. In general, the 6-exo-dig mode of cyclization is facile and is independent of electronic factors. With some of the alkynols, a regioselective (7-endo?) hydration of the alkyne unit was observed and this has been attributed to the participation of C(3)-OH. When the C(3)-OH was protected as its benzyl ether, cycloisomerization of these alkynols occurred exclusively in a 6-exo-dig mode resulting in the corresponding [3.2.1]-bicyclic ketals. Additional control experiments conducted were in support of the participation of C(3)-OH in regioselective alkyne hydration. (C) 2009 Elsevier Ltd. All rights reserved.

%B Tetrahedron %I PERGAMON-ELSEVIER SCIENCE LTD %C THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND %V 65 %P 9819-9832 %8 NOV %G eng %N 47 %3

Foreign

%4

3.011

%R 10.1016/j.tet.2009.09.071