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2005
Pyran derivatives
R 0340
New Synthetic Approach to Cyclopenta-Fused Heterocycles Based upon a Mild
Reaction. Part 2. Further Studies on the Torquoselectivity. — Under
12- 139 Nazarov
mild acidic conditions the conjugated alkoxytrienes (III) undergo Nazarov cyclization
to afford fused cyclopentanones. The reaction proceeds with modest to good diastereoselectivity. In some cases spirocyclic by-products are formed. The product ratio is dependent on steric and stereoelectronic effects. The pyrrole derivatives (XI) and (XIV)
do not undergo direct Nazarov cyclization. However, after subsequent treatment with
neat TFA the desired fused cyclopentanones can be obtained with high diastereoselectivity. — (PRANDI*, C.; FERRALI, A.; GUARNA, A.; VENTURELLO, P.;
OCCHIATO, E. G.; J. Org. Chem. 69 (2004) 22, 7705-7709; Dip. Sci. Ambiente Vita,
Univ. Piemonte Orientale "Amedeo Avogadro", I-15100 Alessandria, Italy; Eng.) —
Jannicke
2005
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