NOVEL TOCOPHEROL COMPOUNDS IX. SYNTHESIS OF 5a-FUNCTIONALIZED TOCOPHEROLS WITH ORGANOELEMENT SUBSTITUENTS

Abstract

5a-Substituted tocopherols bearing silicon, sulfur, or phosphorus moieties at position 5a have been synthesized starting from 5a-bromo-α-tocopherol (5). 5a-Trialkylsilyl-α-tocopherols (6, 7) were obtained by a sonochemically catalyzed reaction as the key step. Reaction of 5a-bromo-α-tocopherol with N-substituted thioureas provided satisfying yields of the corresponding 5a-α-tocopheryl-thiouroniurn salts (8–10). whereas the reaction with thiols did not produce the 5a-substituted products, but a complex mixture of products due to the occurrence of uncontrollable redox processes during the reaction. Tocopheryltriphenylphosphonium bromide (11) was obtained by a simple quaternization reaction, and has been further exploited as a useful intermediate in the syntheses of novel vitamin E derivatives (12-18) with the tocopherol unit being incorporated into a stable furobenzopyran structure.

Key Words:

• vitamin E
• 5a-substituted tocopherols
• furobenzopyrans
• sonochemistry
• Wurtz-coupling
• intramolecular Wittig reaction