Joan Bosch

Stereoselective Conjugate Addition Reactions to Phenylglycinol‐Derived, Unsaturated Oxazolopiperidone Lactams

Phenylglycinol-derived, unsaturated oxazolopiperidone lactams are extremely useful building blocks that undergo stereoselective conjugate addition reactions with organocuprates, enolates, and sulfur-stabilized anions, allowing the stereocontrolled introduction of substituents at the piperidine 4-position. The factors governing the exo- or endo-facial selectivity are discussed. The methodology can be used for the preparation of a variety of enantiopure piperidines, including pharmaceuticals, alkaloids precursors, piperidine-fused derivatives, as well as complex piperidine-containing natural products.

Enantioselective formal synthesis of ent-rhynchophylline and ent-isorhynchophylline

Starting from (S)-tryptophanol, a formal synthesis of ent-rhynchophylline and ent-isorhynchophylline, involving stereoselective cyclocondensation, spirocyclization, and alkylation reactions, and the final adjustment of the oxidation level at the oxindole and piperidine moieties, is reported.

Total synthesis of (+)-madangamine D.

Madangamines are a group of bioactive marine sponge alkaloids, embodying an unprecedented diazapentacyclic skeletal type. The enantioselective total synthesis of madangamineu2005D has been accomplished, and represents the first total synthesis of an alkaloid of the madangamine group. It involves the stereoselective construction of the diazatricyclic ABC core using a phenylglycinol-derived lactam as the starting enantiomeric scaffold and the subsequent assembly of the peripheral macrocyclic rings. The synthesis provides, for the first time, a pure sample of madangamineu2005D and confirms the absolute configuration of this alkaloid family.

First enantioselective synthesis of tetracyclic intermediates en route to madangamine D

The enantioselective synthesis of advanced tetracyclic precursors of madangamine D, bearing rings ABCD of this alkaloid, is reported. The saturated 14-membered ring is assembled from functionalized diazatricyclic intermediates following either ring-closing metathesis or macrolactamization strategies.

Enantio‐ and Diastereoconvergent Cyclocondensation Reactions: Synthesis of Enantiopure cis‐Decahydroquinolines

Up to four stereocenters with a well-defined configuration are generated in a single synthetic step by the cyclocondensation of (R)-phenylglycinol or (1S,2R)-1-amino-2-indanol with stereoisomeric mixtures (racemates, meso forms, diastereoisomers) of cyclohexanone-based δ-keto-acid and δ-keto-diacid derivatives in enantio- and diastereoconvergent processes that involve dynamic kinetic resolution and/or desymmetrization of enantiotopic groups. A detailed analysis of the stereochemical outcome of this process is presented. This method provides easy access to enantiopure 8- and 6,8-substituted cis-decahydroquinolines, including alkaloids of the myrioxazine family.

Stereoselective synthesis of (−)-lepadins A–C

A concise synthesis of the marine alkaloids (-)-lepadins A-C from a phenylglycinol-derived tricyclic lactam is reported. Key steps from the stereochemical standpoint involve stereoselective cyclocondensation, double bond hydrogenation, oxazolidine opening, hydroboration-oxidation, and Horner-Wadsworth-Emmons reactions.

Enantioselective Synthesis of Lepadins A–D from a Phenylglycinol‐Derived Hydroquinolone Lactam

The marine alkaloids (-)-lepadins A-C and (+)-lepadin D, belonging to two diastereoisomeric series, were synthesized from an (R)-phenylglycinol-derived tricyclic lactam via a common cis-decahydroquinoline intermediate. Crucial aspects of the synthesis are the stereochemical control in the assembly of the cis-decahydroquinoline platform, in the introduction of the C2 methyl and C3 hydroxy substituents, and in the generation of the C5 stereocenter.

Stereoselective Total Synthesis of the Putative Structure of Nitraraine

After the structure originally proposed for nitraraine was shown to be incorrect by total synthesis, the alternative structure 5 was recently suggested for the alkaloid on biosynthetic grounds and by comparison with the (1)H NMR data of tangutorine. The unambiguous synthesis of 5 is reported from tryptophanol and ketodiester 6, via oxazoloquinolone lactam 7. However, the melting point and (1)H NMR data of 5 did not match those reported for the natural product.

Enantioselective Total Synthesis of Fluvirucinin B1

A convergent synthesis of fluvirucinin B1 from acid ent-6a and nitrile ent-9, involving an organocopper coupling, a stereoselective allylation, a ring-closing metathesis reaction, and a stereoselective hydrogenation as the key steps, is reported. The starting building blocks have been prepared in a straightforward manner from a common phenylglycinol-derived lactam 1. An unprecedented regioselective oxidation of phenylglycinol-derived secondary amines 5 to carboxylic acids 6 has been developed.

Enantioselective Total Synthesis of (+)-Gephyrotoxin 287C

A synthesis of (+)-gephyrotoxin 287C using (S)-phenylglycinol-derived tricyclic lactam 7 as the starting enantiomeric scaffold is reported. From the stereochemical standpoint, the key steps are the generation of the DHQ C-5 stereocenter by hydrogenation of the C-C double bond, removal of the chiral inductor to give a cis-DHQ, introduction of the DHQ C-2 substituent, completion of the (Z)-enyne moiety, and generation of the C-1 stereocenter during closure of the pyrrolidine ring.