Gerd Dürner

Total synthesis of (1S,4S)-7,8-dihydroxycalamenene via benzylic alkylation of η6-arene-Cr(CO)3 complexes

Abstract The enantioselective total synthesis of the antiinfective sesquiterpene (1S,4S) -7,8-dihydroxy-calamenene ( 4 ) is accomplished by a strategy which centrally utilizes the reactivity of arene-Cr(CO) 3 complexes. In a sequence involving two successive benzylic deprotonation/alkylation steps, the chiral complex 8 (> 99% e.e.) is converted completely regio- and diastereoselectively to 7 and further by decomplexation and ether cleavage to the target compound 4 in high overall yield and without loss of enantiomeric purity.

Chiral η6-arene-Cr(CO)3 complexes as synthetic building blocks : an enantio- and diastereoselective approach to substituted hydrophenalenes related to helioporin E and pseudopterosin G

Abstract The enantioselective total synthesis of compound 14 , an analogue of dihydro-helioporin E and dihydro-pseudopterosin G, is accomplished by a strategy which centrally relies on the reactivity of arene-Cr(CO) 3 complexes. The chiral synthetic building block 6 (> 97 % e.e.) is converted in 12 steps regio- and diastereo-selectively into complex 12 , from which 14 is obtained by decomplexation and methylation. Key steps of the synthesis are two succesive regio- and diastereoselective benzylic deprotonation/alkylation reactions.

An enantioselective version of the AB+B→ABCD-type steroid total synthesis

Abstract Diene 1 and dienophile 4a in a Diels/Alder reaction mediated by a chiral ligand-modified Lewis acid enantioselectively furnish adduct 5a (chem. yield: 64%; e.e.: 73%), which after partial deoxygenation and final enantioselection by recrystalization affords 5b. The latter compound can easily be converted via Torgovs pentaenone 6a into estrogens or progestogens.

Enantioselective Synthesis of (+)-Estrone Exploiting a Hydrogen Bond-Promoted Diels−Alder Reaction

Starting from Dane’s diene and methylcyclopentenedione, (+)-estrone is synthesized along the Quinkert−Dane route in 24% total yield. The key step is an enantioselective Diels−Alder reaction promoted by an amidinium catalyst as efficiently as by a traditional Ti-TADDOLate Lewis acid.

E. Dane's route to estrone revisited

Abstract The chirogenic Dieis/Alder reactions of the general pattern AB + D → ABCD, (i): 2 + 3 → rac- 8a (major) + rac- 9a (minor) (85%), (ii): 2 + 10a → rac- 11a (89%), and (iii): 2 + 10b → rac- 11b (90%),now have been accomplished in the presence of Lewis acid, (i): BF3, OEt2, (ii) or (iii): TiCl 4 . Case (iii) may be used as the initial move towards (±)-norgestrel (rac- 14 ).

Reduction of conformational space by 1,2-diketone.Lewis acid chelates

Abstract Various 1,2-diketones function as chelating ligands with Ti and Sn, but not with Al Various 1,2-diketones function as chelating ligands with Ti and Sn, but not with Al.

An approach to chiral η4-butadiene-Fe(CO)3 complexes via diastereoselective complexation of nonracemic 2-alkoxy-4-vinyl-2,5-dihydrofuran derivatives

Abstract Complexation of (+)-L-arabinose-derived 2-benzyloxy-4-vinyl-2,5-dihydrofuran derivatives (8) with Fe2(CO)9 in ether proceeds diastereoselectively providing a (separable) mixture of the corresponding exo- and endo-η4-diene-Fe(CO)3 complexes 9 and 10 in a ratio of about 1 : 3. The relative (and absolute) configuration of the complexation products was determined by a combination of analytical methods (CD, NMR, X-ray).

Enantioselective Conjugate Addition Greatly Improves the Synthesis of (+)-Confertin

Abstract Enantioselective realization of the chirogenic isopropenylation of 1 (chem.yield:88%), mediated by a ligand-modified organocuprate: The five-membered ring building blocks 2+3 are enantioselectively produced by conjugate addition of a chiral ligand-modified organocuprate to 2-methylcyclopent-2-enone (1) (chemical yield: 88%; e.e.: 88%) and successfully converted in a multi-step sequence, after final enantioselection by recrystallization of an appropriate intermediate, into the pseudoguaianolide (+)-confertin (5).

Substantial refinement of the photochemical synthesis of (+)-Aspicillin

Abstract The photochemical synthesis of the 18-membered lichen macrolide (+)-aspicilin ( 1a ), reported earlier, is characterized by the successful use of a photolactonization as a key reaction and by diastereoselective generation of stereogenic centers C(4), C(5), and (C(6). In comparison with an especially designed reference synthesis, where all the stereogenic centers came from the chiral pool, the photochemical synthesis of 1a needs further refinement. This has been achieved now by the use of ortho -formyl benzoic acid as a nucleophile in a Pd(0)-mediated epoxide ring opening furnishing an ester which is known easily to be hydrolyzed by morpholine catalysis.

Cleavage of Phosphodiesters and of DNA by a Bis(guanidinium)naphthol Acting as a Metal-Free Anion Receptor

Phosphoric acid diesters form anions at neutral pH. As a result of charge repulsion they are notoriously resistant to hydrolysis. Nucleophilic attack, however, can be promoted by different types of electrophilic catalysts that bind to the anions and reduce their negative charge density. Although in most cases phosphodiester‐cleaving enzymes and synthetic catalysts rely on Lewis acidic metal ions, some exploit the guanidinium residues of arginine as metal‐free electrophiles. Here we report that a combination of two guanidines and a hydroxy group yields highly reactive receptor molecules that can attack a broad range of phosphodiester substrates by nucleophilic displacement at phosphorus in a single‐turnover mode. Some stable O‐phosphates were isolated and characterized further by NMR spectroscopy. The bis(guanidinium)naphthols also cleave plasmid DNA, presumably by a transphosphorylation mechanism.