Scalable Synthesis of Oxazolones from Propargylic Alcohols through Multistep Palladium(II) Catalysis: β-Selective Oxidative Heck Coupling of Cyclic Sulfonyl Enamides and Aryl Boroxines
作者:Santosh Kumar Alamsetti、Andreas K. Å. Persson、Tuo Jiang、Jan-E. Bäckvall
DOI:10.1002/anie.201307471
日期:2013.12.16
unusual β selectivity to generate a variety of branched substituted oxazolones (see scheme; Ts=p‐toluenesulfonyl). The three‐step synthesis from readilyavailable starting materials with a simple palladium catalyst and inexpensive reagents could be carried out in a single reaction vessel or scaled up for the preparation of large amounts of these amino acid precursors.
On treatment with catalytic amounts of gold(I) chloride (AuCl) and a base co-catalyst, O-propargyl carbamates smoothly undergo a 5-exo-dig cyclization at room temperature to afford 4-methylene-2-oxazolidinones in high yield. Substrates with a substituent at the alkyne terminus stereoselectively give rise to (Z)-4-alkylidene-2-oxazolidinones.