Intramolecular Chromium(II)-Catalyzed Pinacol Cross Coupling of 2-Methylene-α,ω-dicarbonyls
作者:Ulrich Groth、Marc Jung、Till Vogel
DOI:10.1055/s-2004-822895
日期:——
Using only 10% of CrCl2 as catalyst, manganese-powder as reducing agent and TMSCl as scavenger, 2-methylene-α,Ï-dialdehydes and -ketones can be coupled to form cyclic diols diastereoselectively. The diastereomeric excess strongly depends on the ring size and the substituents of the Ï-carbonyl group. The greater the ring size the higher diastereoselectivities are observed. In all cases cis-diols are preferentially formed.
Total Syntheses of (<i>S</i>)-(−)-Zearalenone and Lasiodiplodin Reveal Superior Metathesis Activity of Ruthenium Carbene Complexes with Imidazol-2-ylidene Ligands
作者:Alois Fürstner、Oliver R. Thiel、Nicole Kindler、Beata Bartkowska
DOI:10.1021/jo0009999
日期:2000.11.1
can be obtained either via a Stille cross-coupling reaction of tributylvinylstannane or, even more efficiently, by Heck reactions of the aryl triflate precursors with pressurized ethene. Furthermore, the synthesis of 1 via RCM is compared with an alternative approach employing a low-valent titanium-induced McMurry coupling of dialdehyde 47 for the formation of the large ring. This direct comparison
Highly Diastereoselective Synthesis of <i>vicinal</i> Quaternary and Tertiary Stereocenters Using the Iodo-aldol Cyclization
作者:Frederic Douelle、Amy S. Capes、Michael F. Greaney
DOI:10.1021/ol070482k
日期:2007.5.1
The intramolecular iodo-aldol cyclization of alpha-substituted enoate aldehydes and ketones is described. Using prochiral starting materials, the reaction produces hetero- and carbocycles containing quaternary centers adjacent to secondary or tertiary centers. The reactions occur in good yields and are highly selective for the trans-products, having the hydroxyl and iodomethyl groups on opposite faces of the ring system.