152978-83-1Relevant articles and documents
A Stereospecific Access to Allylic Systems Using Rhodium(II)-Vinyl Carbenoid Insertion into Si-H, O-H, and N-H Bonds
Bulugahapitiya, Priyadarshanie,Landais, Yannick,Parra-Rapado, Liliana,Planchenault, Denis,Weber, Valery
, p. 1630 - 1641 (2007/10/03)
Rhodium-catalyzed decomposition of α-vinyldiazoesters in the presence of silanes, alcohols, ethers, amines, and thiols have been shown to produce the corresponding α-silyl, α-hydroxy, α-alkoxy, α-amino, and α-thioalkoxy esters in generally good yield with a complete retention of the stereochemistry of the double bond of the diazo precursor. An extension of the process in homochiral series has also been devised using either a chiral auxiliary attached to the ester function or achiral α-vinyldiazoesters and Doyle's chiral catalyst Rh2(MEPY)4. In the former approach, pantolactone as chiral auxiliary gave diastereoselectivities of up to 70%, while the second approach produced the desired allylsilane with ee as high as 72%. On the other hand, Rh2(MEPY)4-catalyzed insertion into the O-H bond of water led to poor or no enantioselectivity in good agreement with recent literature reports.
α-Hydroxy esters as chiral auxiliaries in asymmetric cyclopropanations by rhodium(II)-stabilized vinylcarbenoids
Davies, Huw M. L.,Huby, Nicholas J. S.,Cantrell Jr., William R.,Olive, Jennifer L.
, p. 9468 - 9479 (2007/10/02)
The use of several α-hydroxy esters as chiral auxiliaries for asymmetric cyclopropanation with rhodium-(II)-stabilized vinylcarbenoids is presented. Use of either (R)-pantolactone or (S)-lactate allowed entry into both series of enantiomeric vinylcyclopropanes with predictable absolute stereochemistry. Steric and electronic modifications of the chiral auxiliary as well as catalyst structure were shown to have major effects on the asymmetric induction. These results were rationalized on the basis of an interaction between the carbonyl oxygen of the chiral auxiliary and the carbenoid carbon. By combining the asymmetric cyclopropanation with a subsequent Cope rearrangement, an enantioselective entry into hydroazulenes was achieved. The potential of the asymmetric cyclopropanation was illustrated by a short synthesis of (1R,2R)-2-phenylcyclopropane amino acid 5.
