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2001
ring closure reactions
ring closure reactions
O 0130
The Preparation and Evaluation of Electron-Poor Benzylidene
16 - 059 Fischer Carbene Complexes: Studies Toward the Total Synthesis
of (+)-Olivin.
— The benzanellation reaction of various electron-poor
benzylidene Fischer carbene complexes (I) and (V) with simple alkynes is studied. It is shown, that electron-withdrawing substituents at the para-position
increase the chemoselectivity towards six-membered ring formation [cf. (IIIa)],
while with a strongly electron-donating para-substituent appreciable amounts
of five-membered ring formation [cf. (VI)/(VII)] are observed. Additionally, a
larger alkoxy group at the carbene carbon increases the yield of the expected
product [cf. (IIIb) vs. (IIIc)]. These effects, however, are not observed for
carbene complexes containing ortho-substituents. The presented methodology
can be successfully applied to create a novel key step [(XII)→(XVI)] for
the olivin synthesis. — (LIPTAK, VINCENT P.; WULFF, WILLIAM D.;
Tetrahedron 56 (2000) 52, 10229-10247; Dep. Chem., Univ. Chicago, Chicago,
IL 60637, USA; EN)
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2001
ring closure reactions
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