Carbohydrate-derived 4-pentyn-1-ols have been synthesized from spirocyclic oxirane precursors upon reaction with allenylmagnesium bromide. They undergo cycloisomerization at low-valent chromium or tungsten templates to give spirocyclic 2-oxacyclohexylidene metal complexes. (C) 2000 Elsevier Science S.A. All rights reserved.
Carbohydrate-derived 4-pentyn-1-ols have been synthesized from spirocyclic oxirane precursors upon reaction with allenylmagnesium bromide. They undergo cycloisomerization at low-valent chromium or tungsten templates to give spirocyclic 2-oxacyclohexylidene metal complexes. (C) 2000 Elsevier Science S.A. All rights reserved.
Cycloisomerization of Alkynols at Transition Metal Templates
The metal-assisted cycloisomerization of ω-alkynols to oxacycloalkylidene complexes is reviewed. A variety of low-valent coordinatively unsaturated transitionmetal templates from group 6 to 10 mediate the cyclization of ω-butynols, -pentynols, and -hexynols to give the corresponding oxacycloalkylidene complexes. In some cases kinetic hydroxyalkylvinylidene complex intermediates can be isolated and