Scaffold Decoration of C-Glycosides

The group of John A. Porco, Jr. and Scott E. Schaus from Boston University has reported on the synthesis of aryl ether C-glycoside derivatives 3 via Pd(0)-mediated allylic substitution of biscarbonates 1 with phenols 2 (Org. Lett. 2006, 8, 5065. DOI: 10.1021/ol0618252). This reaction was both regio- and stereoselective with an overall retention of configuration when the enantiomeric (S,S)-Trost ligand was employed. The protected aryl ether C-glycosides 4 can be further diversified by Eu(III)-catalyzed Claisen rearrangement where glycosides 4 undergo a [3,3]-sigmatropic rearrangement and furnish the novel phenol derivatives 5.

Synthesis of 2-Amino-dihydropyrimidin-4-ones

The three-component reaction of Meldrum´s acid (1), aldehydes 2 and guanidine carbonate (3) for the simple synthesis of 2-amino-dihydropyrimidines 4 was developed by Nikolay Yu. Gorobets and co-workers from the National Academy of Scienes of Ukraine (Mol. Diversity 2006, 10, 483. DOI: 10.1007/s11030-006-9045-1). The reactions were performed both under conventional (120-130 °C, 20-25 min) and microwave heating (150 °C, 5 min) showing slightly higher yields for most of the derivates applying conventional conditions. Importantly, to avoid high pressure build up in the closed microwave vials due to CO₂ formation, the reaction mixture was stirred for 10-15 min at rt before subjecting to microwave irradiation.

Cross-Coupling of Arylboronic Acids with Acid Chlorides

A set of 19 symmetrical and unsymmetrical aryl ketones was prepared via Suzuki coupling of arylboronic acids with acid chlorides in moderate to high yields under very mild reaction conditions (98 °C, 10 min) by the group of Viera Poláčková from Comenius University in Bratislava (Tetrahedron 2006, 62, 11675. DOI: 10.1016/j.tet.2006.09.055). A catalyst screen for the reaction of phenylboronic acid and 4-nitrobenzoyl chloride revealed that Pd(PPh₃)₄ and Cs₂CO₃ as catalyst/base system provided the aryl ketone (R¹ = Ph, R² = 4-NO₂-Ph) in highest yield under the given microwave-conditions.

Synthesis of Tricyclic Symmetrical and Unsymmetrical Heterocycles

Mark Lautens and co-workers from the University of Toronto have investigated the synthesis of tricyclic heterocycles (3 and 4) starting from aryl iodide 1 which contains two tethered alkyl bromides and a Heck acceptor 2 or Zn(CN)₂, respectively. Products 3 are obtained via a norbornene-mediated Pd-catalyzed intramolecular bis-alkylation/intermolecular alkenylation sequence of 1 and 2 (Synlett 2006, 2969. DOI: 10.1055/s-2006-941583) whereas tricyclic benzonitriles 4 are received via tandem intramolecular bis-alkylation/intermolecular cyanation reaction applying the same catalytic system (J. Am. Chem. Soc. 2006, 128, 14436. DOI: 10.1021/ja064742p).