2001 vitamins

vitaminsU 0900

05 - 218Stereocontrolled Synthesis of 6-s-cis- and 6-s-trans-Locked 9Z-Retinoids by Hydroxyl-Accelerated Stille Coupling of (Z)-Tri-n-butylstannylbut-2-en-1-ol and Bicyclic Dienyl Triflates. — Thetitle reaction proceeds successfully under mild conditions (25 ◦C, 30 min). Incontrast, Stille coupling of (E)-isomers like (XI) and (XIII) requires heating andlonger reaction times. Intramolecular coordination of the (Z)-hydroxy groupto Pd-catalyst is responsible for the considerable rate difference exhibited by(Z)- and (E)-alkenylstannanes. Additionally, it is shown that the (9Z)-retinoidsundergo facile isomerization to the (E)-isomers in the presence of iodine. —(DOMINGUEZ, BEATRIZ; PAZOS, YOLANDA; DE LERA, ANGEL R.; J.Org. Chem. 65 (2000) 19, 5917-5925; Dep. Quim. Org., Univ. Vigo, E-36200Vigo, Spain; EN)

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