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2005
Fused 6,6,5-ring systems
Q 1070
New Procedure for the Preparation of Highly Sterically Hindered Alkenes Using
Hypervalent Iodine Reagent. — A new method to prepare sterically overcrowded
20- 093 aalkenes
and molecular motors is reported. The target alkenes consist of distinct upper
and lower halves. In the upper half they contain a five-membered ring bearing the
stereocenter needed to control the direction of the molecular motor rotation. The route
to target alkenes involves the generation of the diazo compound from hydrazone (I) by
treatment with hypervalent iodine reagent, followed by a 1,3-dipolar cycloaddition/
dinitrogen elimination/ring closure reaction with cyclic thioketones, and final desulfuration of the resulting episulfides. The present method allows selective coupling of
different upper and lower halves without formation of homocoupled products. The desulfuration step is followed in most cases by an additional reaction with MeI to separate
the excess of PPh3 which is not separable by chromatographic methods. — (TER
WIEL, M. K. J.; VICARIO, J.; DAVEY, S. G.; MEETSMA, A.; FERINGA*, B. L.;
Org. Biomol. Chem. 3 (2005) 1, 28-30; Dep. Org. Mol. Inorg. Chem., Univ.
Groningen, NL-9747 AG Groningen, Neth.; Eng.) — Klein
2005
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