Shyh-Pyng Huang

A stereoselective synthesis of corynantheine-type alkaloids via enamine annulation. Total synthesis of (±)-dihydrocorynantheol and formal total synthesis of (±)-corynantheine and (±)-ajmalicine

Enamine annulation between 3,4-dihydro-1-methyl-β-carboline (4) and dimethyl 3-methoxyallylidenemalonate (5) yielded 2-(2,2-dimethoxyethyl)-2,3,4,6,7,12-hexahydro-3-methoxycarbonyl-4-oxoindolo [2,3-a]quinolizine (6), which was transformed into (±)-dihydrocorynantheol (1). (±)-Corynantheal (19), which is convertible into (±)-corynantheine (2) and (±)-ajmalicine (3), was stereoselectively synthesised from (6)via empimerisations at the angular position using Adams catalyst.

Total synthesis of (±)-epithienamycins A and B [(±)-olivanic acids MM22380 and MM22382] and derivatives

(±)-(3R*,4R*)-4-(2,2-Dimethoxyethyl)-3[(1S*)-1-hydroxyethyl]azetidin-2-one (7), which has been stereoselectively synthesised via the 4-methoxycarbonylisoxazoline (4), was converted into (±)-epithienamycins A (2) and B (3)[(±)-olivanic acids MM22380 and MM22382], (±)-deacetylepithienamycin A (20), and the 2-phenylthio-substituted compound (19). This total synthesis confirms the relative stereochemistry of the natural antibiotics.

Studies on the syntheses of heterocyclic compounds. Part 877. An alternative synthesis of protected (±)-thienamycin and a related compound

An alternative total synthesis of protected (±)-thienamycin (2) and an analogue is described. (±)-4β-(2,2-Dimethoxyethyl)-3α-[(1R*)-1-(p-nitrobenzyloxycarbonyloxy)ethyl]azetidin-2-one (5), prepared from isoxazoline derivatives (4), was converted into the 2-(p-nitrobenzyloxycarbonylamino)ethyl (12) and phenyl (13) thioester phosphoranes. Intramolecular Wittig reaction of (12) and (13) produced the corresponding carbapenems (2) and (3) in poor yield. Effective transformation of (5) into the p-nitrobenzyl-protected thienamycin derivative (2) and the analogue (3) was achieved employing a carbene insertion reaction and subsequent introduction of the sulphide moiety.

Studies on the syntheses of heterocyclic compounds. Part 683. Stevens rearrangement of berbine methiodides by sodium bis-(2-methoxyethoxy)aluminium hydride

Refluxing berbine methiodides with sodium bis-(2-methoxyethoxy)aluminium hydride in dioxan resulted in Stevens rearrangements to afford spirobenzylisoquinolines and 8-methylberbines. The stereochemistry at the migrating carbon atom and the relationship between the configuration of the starting quinolizidinium salts and the products have been studied.