Syntheses of Stereochemically Diverse Nine-Membered Ring-Containing Biaryls
摘要:
A library of nine-membered, biaryl-containing rings has been synthesized in parallel on polystyrene macrobeads. Dimeric medium rings were shown to be accessible via a regio- and stereoselective double cyclization.
Practical catalyst for cyclic metathesis. Synthesis of functional and/or enantiopure cycloalkenes.
摘要:
The oxo-tungsten complex trans-WOCl2(OAr)(2) (Ar = 2,6-dibromophenyl) is prepared by reaction of WOCl4 with 2 equiv of 2,6-dibromophenol. A variety of nonconjugated dienes are cleanly cyclized to the corresponding cycloalkenes using 2 mol % of this catalyst in combination with 4 mol % of tetraethyllead. All three components of the catalyst system are commercially available. The catalytic reactions are typically complete in 1 h at 90 degrees C and allow the synthesis of chiral cycloalkenes with little or no loss in optical activity. For example, (R)- (S)-citronellene have been cyclized to the corresponding (R)- or (S)-3-methylcyclopentenes in 97% enantiomeric excess. The cyclization is compatible with a variety of functional groups including some eater, amide, and ether derivatives. Tri- (but not tetra-) substituted cycloalkenes could be prepared using this catalyst.
Thioallenoates in catalytic enantioselective [2+2]-cycloadditions with unactivated alkenes
作者:Michael L. Conner、Johannes M. Wahl、M. Kevin Brown
DOI:10.1016/j.tet.2019.04.028
日期:2019.6
The application of thioallenoates to catalytic enantioselective [2+2]-cycloadditions with unactivated alkenes is reported. In many cases, the thioallenoates examined exhibit superior reactivity and selectivity compared to the allenic esters generally used in these cycloadditions.