Structural revision of stemoburkilline from an E-alkene to a Z-alkene.

Phytochemical studies on Stemona burkillii prain: two new dihydrostemofoline alkaloids.

Two new dihydrostemofoline alkaloids, 11(S),12(R)-dihydrostemofoline (3) and stemoburkilline (4), along with stemofoline (1) and 2'-hydroxystemofoline (2) have been isolated from a root extract of Stemona burkillii Prain. The structure and relative configuration of 3 have been determined via spectroscopic data and from comparison with synthetic 11(S),12(S)-dihydrostemofoline (5). The configurat...

A Novel Isomerization of an Electron-Rich Alkene

Organoiron Complexes, Olefin Isomerization, 1,2-Dimethoxyethylene Displacement of 2-methvlpropene from [Fp(Me2C = CH2)]BF4 (Fp = (/?5-C5H5)Fe(CO)2) by Z-1,2-dimethoxyethylene (Z-DME) gives [Fp(Z-DME)]BF4. Displacement by E-1,2dimethoxyethylene (E-DME), in contrast, does not give the expected complex of E-DME, but rather the complex of the Z-alkene. A mechanism involving scission of the C = C bo...

Enantioselective intramolecular hydroarylation of alkenes via directed C-H bond activation.

Highly enantioselective catalytic intramolecular ortho-alkylation of aromatic imines containing alkenyl groups tethered at the meta position relative to the imine directing group has been achieved using [RhCl(coe)2]2 and chiral phosphoramidite ligands. Cyclization of substrates containing 1,1- and 1,2-disubstituted as well as trisubstituted alkenes were achieved with enantioselectivities >90% e...

Intramolecular Nitrogen Delivery for the Synthesis of C-Glycosphingolipids. Application to the C-Glycoside of the Immunostimulant KRN7000

The key reaction in this approach to C-glycosphingolipids is the stereoselective iodocyclization of a sugar-linked homoallylic carbonimidothioate. E and Z reaction substrates were assembled in a convergent fashion via an alkene metathesis strategy and exhibited the same alkene facial selectivity in the iodocyclization irrespective of alkene geometry, although the E alkene was found to be less r...

I. An Improved Procedure for Alkene Ozonolysis. II. Exploring a New Structural Paradigm for Peroxide Antimalarials