Gerhard Quinkert

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.

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.

δ‐Peptide Analogues of Pyranosyl‐RNA, Part 1 , Nucleo‐δ‐peptides Derived from Conformationally Constrained Nucleo‐δ‐amino Acids: Preparation of Monomers

Cyclic nucleo-δ-amino acids that constitute monomers of a conformationally constrained nucleo-δ-peptide base-pairing system have been prepared. Their synthesis starts with an enantioselectively catalyzed chirogenic Diels-Alder reaction, proceeds via a regioselective e-iodolactamization process, and ends with a regio- as well as diastereoselective introduction of nucleobases through SN2-type opening of a transiently formed N-acylaziridine ring. Extensive use of X-ray crystal-structure analysis has been made to support structure assignments.

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.

Photolactamization: A Novel Synthetic Entry into Large Ring-Sized Lactams

Abstract Diene ketenes smoothly accessible by photochemical ring cleavage of o-quinol acetates, in the presence of primary or secondary amines afford the corresponding amides. In an intramolecular version of this reaction macrocyclic lactams of type A are produced, if aminoalkylated o-quinol acetates of type C are used as photo reactants. These photo reactants are available on acid mediated removal of the Boc-protecting group from Wessely acetoxylation products of type D, easily formed via compounds of type E from aminoalkylated phenols of type F.

Progress in the Diels/Alder Reaction Means Progress in Steroid Synthesis

The case history of achiral cantharidin reveals the development of unusual conditions under which the Diels/Alder reaction can play the key synthetic part.