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2005
Multi-membered O,S-heterocycles
R 0691
Ring Closing Enyne Metathesis: Control over Mode Selectivity and Stereoselec— Enynes bearing tartrate-derived linker to attach ene and yne moieties undergo
08- 177 tivity.
ring closing metathesis (RCM) with an exo/endo selectivity depending on the ring size
of the resulting products. Thus 11-membered endo-product (IVa) is formed exclusively
from enyne (Ia), whereas larger rings are formed predominantly as exo-products. The
E/Z selectivity of the resultant macrocyclic 1,3-dienes is not predictable except for
10- and 11-membered rings. Both, the exo/endo-mode selectivity of the ring closure
and the E/Z-selectivity of the 1,3-dienes are improved by performing these reactions
under ethylene atmosphere. In the presence of ethylene, enynes (I) undergo cross metathesis to give isolable acyclic 1,3-dienes, which further react by a diene RCM to afford
exclusively the endo-products with high E-selectivity (to be continued). —
(HANSEN, E. C.; LEE*, D.; J. Am. Chem. Soc. 126 (2004) 46, 15074-pp; Dep.
Chem., Univ. Wis., Madison, WI 53706, USA; Eng.) — Klein
2005
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