M. Vandewalle

Iridoids: enantioselective synthesis of loganin via an asymmetric Diels-Alder reaction

Abstract Starting from (-)-camphor-10-sulfonic acid ( 5 ) the crystalline sultam 9 was readily prepared. TiCl4-mediated Diels-Alder addition of the N-crotonoyl sultam 11 to cyclopentadiene, crys- tallization of the resulting adduct 12 and subsequent reduction gave virtually pure (1S, 4R, 5R, 6S)- 1 together with recovered auxiliary 9 . The loganin precursor 1 was transformed into norbornanone 20 , which upon Baeyer-Villiger oxidation led to the suitably substituted cyclo- pentane 22 from which 1-B-O-methyl loganin aglucone ( 2 ) was rea- dily available.

An Efficient Preparation and the Intramolecular Cyclopropanation of a-Diazo-3-Ketophosphonates and a-Diazophosphonoacetates

Abstract An improved method for the preparation of the title compounds is presented. Several catalysts have been studied for the cyclopropanation reaction; the best results (n = 40-76 %) have been obtained with copper powder in re-fluxing cyclohexane.

Photoinduced Wolff Rearrangement of α-Diazo-β-Ketophosphonates : A Novel Entry into Substituted Phosphonoacetates

Abstract Direct irradiation (254 nm) of α-diazo-β-ketophosphona-tes in the presence of an alcohol, leads to substituted phosphonoacetates. This allows a novel construction of the functionalized isopropyl group present in many ses-quiterpenes.

Enantioselective total synthesis of (−)-epipodophyllotoxin and (−)-podophyllotoxin

Abstract An enantioselective total synthesis of (−)-epipodophyllotoxin (2) and hence of (−)-podophyllotoxin (1) is described, involving as key steps a conjugate addition on butenolide 13 as the chiral template, a stereoselective aldol condensation on 11a and a stereoselective ring closure of 8.

Iridoids: stereospecific synthesis of functionalized cyclopentanoid intermediates via bicyclo [2.2.1] heptanones

Abstract An efficient synthesis of functionalized trialkyl substituted cyclopentanoids is presented. Stereocontrol is secured by their formation from norbornane precusors. The strategy is illustrated by the total synthesis of (±)-boschnialactone ( 13 ), (±)-teucriumlactone C ( 14 ) and (±)-loganin ( 2 ).

The synthesis of 2-azapodophyllotoxins

Abstract 2-Azapodophyllotoxins, tetrahydroisoquinoline analogues of podophyllotoxin have been synthesized. They constitute a new class of highly potent anti-tumor agents.

Bryostatins: The asymmetric synthesis of C1-C9 and C11-C16 fragments

Abstract The fragments C 1 -C 9 19 and C 11 -C 16 26 of the bryostatins are constructed in an enantioselective and highly diastereoselective fashion from respectively D-pantolactone ( 2 ) and L-erythrulose ( 3 ) as chiral templates.

The synthesis of 4-desoxy-2-azapodophyllotoxins

Abstract 4-Desoxy-2-azapodophyllotoxins, tetrahydroisoquinoline analogues of podophyllotoxin, have been synthesized and evaluated for their anti-tumor activities.

An efficient synthesis of 1α, 25-dihydroxy vitamin D3

Abstract An efficient synthesis of the title compound is reported based on C-1 functionalization of the triazoline Diels-Alder adduct of 25-OH provitamin D3 ( 2C ).

Cyclopentanones—VIII : Stereochemistry of the lithium-liquid ammonia reduction of 2,3-dialkyl-4-hydroxy-2-cyclopentenones

Abstract 2,3-Dialkyl-1,4-cyclopentanediols are obtained by lithium-liquidammonia-alcohol reduction of 2,3-dialkyl-4-hydroxy-2-cyclopentenones. The configuration of the diastereoisomers formed was proved by 1H-NMR spectroscopy and by chemical evidence. In the most abundant isomer the alkyl groups are trans and each is in trans position to the vicinal hydroxyl function. In another diastereoisomer formed in substantial amount the alkyl groups have a cis orientation and are trans to the vicinal hydroxyl function. The 1H-NMR parameters found are more useful generally for configurational assignments to synthetic and modified prostaglandins.