Electroreductive intramolecular coupling of aliphatic cyclic imides with α,β-unsaturated esters and ketones: unusual methyl-alkoxy exchange in silyl ketene acetals

Electroreductive Intermolecular Coupling of Uracils with Aromatic Ketones: Synthesis of 6-Substituted and cis-5,6-Disubstituted 5,6-Dihydro-1,3-dimethyluracils and Their Transformation to 6-Substituted 1,3-Dimethyluracils, trans-5,6-Disubstituted 5,6-Dihydro-1,3-dimethyluracils, and 4,5,5-Trisubstituted 3-Methyloxazolizin-2-ones

The electroreductive coupling of 1,3-dimethyluracil, thymine, and 5-fluorouracil with aromatic ketones in the presence of TMSCl gave 6-substituted and cis-5,6-disubstituted 5,6-dihydro-1,3-dimethyluracils. The dehydrotrimethylsiloxylation of the adducts afforded 6-substituted and 5,6-fused 1,3-dimethyluracils. The detrimethylsilylation of the adducts with TBAF or 1 M HCl-MeOH gave 4,5,5-trisubstituted 3-methyloxazolizin-2-ones or 3-methyloxazolizin-2-imines in addition to simply desilylated alcohols. The cis-5,6-disubstituted 5,6-dihydro-1,3-dimethyluracils were isomerized to the corresponding trans-isomers by heating in the presence of cat. DMAP. The cis- and trans-5,6-disubstituted 5,6-dihydro-1,3-dimethyluracils were assigned by the coupling constants J5,6 of their (1)H NMR spectra.

Simple Indolizidine and Quinolizidine Alkaloids

This review of simple indolizidine and quinolizidine alkaloids (i.e., those in which the parent bicyclic systems are in general not embedded in polycyclic arrays) is an update of the previous coverage in Volume 55 of this series (2001). The present survey covers the literature from mid-1999 to the end of 2013; and in addition to aspects of the isolation, characterization, and biological activity of the alkaloids, much emphasis is placed on their total synthesis. A brief introduction to the topic is followed by an overview of relevant alkaloids from fungal and microbial sources, among them slaframine, cyclizidine, Steptomyces metabolites, and the pantocins. The important iminosugar alkaloids lentiginosine, steviamine, swainsonine, castanospermine, and related hydroxyindolizidines are dealt with in the subsequent section. The fourth and fifth sections cover metabolites from terrestrial plants. Pertinent plant alkaloids bearing alkyl, functionalized alkyl or alkenyl substituents include dendroprimine, anibamine, simple alkaloids belonging to the genera Prosopis, Elaeocarpus, Lycopodium, and Poranthera, and bicyclic alkaloids of the lupin family. Plant alkaloids bearing aryl or heteroaryl substituents include ipalbidine and analogs, secophenanthroindolizidine and secophenanthroquinolizidine alkaloids (among them septicine, julandine, and analogs), ficuseptine, lasubines, and other simple quinolizidines of the Lythraceae, the simple furyl-substituted Nuphar alkaloids, and a mixed quinolizidine-quinazoline alkaloid. The penultimate section of the review deals with the sizable group of simple indolizidine and quinolizidine alkaloids isolated from, or detected in, ants, mites, and terrestrial amphibians, and includes an overview of the "dietary hypothesis" for the origin of the amphibian metabolites. The final section surveys relevant alkaloids from marine sources, and includes clathryimines and analogs, stellettamides, the clavepictines and pictamine, and bis(quinolizidine) alkaloids.

Electroreductive coupling of optically active α,β-unsaturated carbonyl compounds with diaryl ketones: asymmetric synthesis of 4,5,5-trisubstituted γ-butyrolactones

The electroreductive coupling of optically active N-E-crotonoyl- and N-cinnamoylimidazolidin-2-ones and oxazolidin-2-ones with diaryl ketones in the presence of chlorotrimethylsilane gave adducts with high diastereoselectivity. The adducts were readily transformed to optically active 4,5,5-trisubstituted γ-butyrolactones by treatment with TBAF.