The azidomethylpyrrolylmethylenepropanedioate (IX), prepared from the pyrrolethiocarboxylate (I) as outlined in the reaction scheme, is cyclized upon treatment with triphenylphosphine to produce the arylsulfonyldihydropyrrolo(3,4‐b)pyrrole (X).
A Friedel-Crafts Cyclization Approach Toward Cephalotaxine.-N-Protection of the azepinone (I) with the anhydride (II) followed by reaction with methyllithium (IV) yields the ring-opened carbinol (V) which is cyclized with 4-toluenesulfonic acid to produce the spiro compound (VI). Ozonolysis of (VI) forms the amino ketone (VII) which is deprotected and then coupled with the sulfonates (VIII) to give the N-alkylation products (IX). Only the derivative (IXa) is cyclized in polyphosphoric acid, producing the cephalotaxine skeleton (Xa). -(SHA, C.-K.; YOUNG, J.-J.; YEH, C.-P.; CHANG, S.-C.; WANG, S.-L.; J.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Tungsten-Promoted Intramolecular Alkoxycarbonylation for Synthesis of Complex Oxygenated Molecules.-Chloroalkynols react with (II) to W-propargyl compounds which undergo intramolecular alkoxycarbonylation to form lactones with excellent diastereoselectivities. With a silyloxy substitution for an α-hydroxy group the lactones (IIIc) and (IIId) are formed as syn products. Starting from D-(+)-xylose the chiral compound (XI) is prepared which gives the optically active lactone (XII) illustrating the stereochemical effect of the silyloxy group. The stereochemistries and reaction mechanisms are discussed in detail. All these lactones can be converted to allylanions that react in situ with aldehydes and ketones forming lactones which are useful materials for syntheses of trisubstituted 1,3-, 1,4-and 1,5-diols. -(CHEN, C.-C.; FAN, J.-S.; SHIEH, S.-J.; LEE, G.-H.; PENG, S.-M.; WANG, S.-L.; LIU, R.-S.; J.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.