Teluretos vinÃlicos: reaÃÃes de acoplamento e investigaÃÃo da regio- e estereoquÃmica da hidroteluraÃÃo de alquinos

AUTOR(ES)

ClÃcio Gomes dos Santos

DATA DE PUBLICAÇÃO

2006

RESUMO

Vinylic tellurides are valuable synthetic intermediates and have recently been used in the total synthesis of many natural products. The hydrotelluration of alkynes is usually the method of choice to prepare Z-vinylic tellurides, in view of the easy access to the starting materials, the high regio- and stereoselectivity of the reaction and the practicality of the experimental procedure. The first part of this work describes an alternative procedure for the preparation of vinylic telurides. Organotellurium trichlorides obtained from the addition of tellurium (IV) tetrachloride to alkynes were efficiently reduced with sodium borohydride and the intermediate organo-tellurolates were transformed into vinylic tellurides with Z-configuration. The tellurides were then coupled with alkynes under PdCl2 and CuI catalysis to give the corresponding chloro-enynes in low yields with retention of the double bond configuration. The same catalytic system was used on the development of an alternative procedure for the preparation of unsubstituted enediynes present is some natural products with important biological activities. By the coupling reaction of a vinyl telluride and propargyllic alcohol the corresponding enediyne was obtained in good yield also with retention of the double bond configuration. The last part of this work describes a systematic study for the hydrotelluration reaction of diynes and terminal alkynes. Regio- and stereoisomeric mixtures were observed, depending upon the alkyne source as well as the reactions conditions

ASSUNTO(S)

quimica teluretos vinÃlicos chloro-enynes vinylic tellurides enediynes cloro-eninos enediinos

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