Chiral Sulfides for Optically Active Three-membered Rings
(-)-Isothiocineole [T2578] and (+)-isothiocineole [T2579] are limonene derivatives and useful chiral auxiliaries for the synthesis of optically active epoxides, aziridines and cyclopropanes. For instance, a sulfur ylide derived from T2578 reacts with aldehydes and tosylimides to afford chiral epoxides and aziridines, respectively, in high diastereo- and enantioselectivity. It is found that this asymmetric reaction can smoothly proceed on a gram scale. Another advantage is that both T2578 and T2579 can be recovered and recycled after the reaction.
Oxidation, which makes its target substance lose electrons, is one of the most basic reactions in organic chemistry and is exemplified by the reaction with oxygen or a dehydrogenation reaction. In particular, oxidizing agents have often been used for the transformation of alcohols to the corresponding aldehydes, ketones or carboxylic acids. Less harmful oxidizing agents without heavy metals have been developed, such as Dess-Martin periodinane, the Mukaiyama oxidizing agent and oxoammonium salts. Moreover, oxidation reactions employing inexpensive cooxidants have been reported in the presence of oxidation catalysts like tetrapropylammonium perruthenate (TPAP) and TEMPO.
The Williamson ether synthesis is an old, but still frequently encountered organic reaction, which provides ether products most often from alcohols and alkyl halides. Alkoxides, derived from alcohols and bases such as sodium hydride are generated in situ, and alkyl halides can react through SN2 type mechanism to give a variety of ether products. The reactivity is generally dependent on the pertinent SN2 reaction, with steric being the dominant factor.
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