Studies towards the total synthesis of hygrocins A and B

The western segment of hygrocins A–B has been synthesized through the coupling of a chiral C5–C13 synthon with the sterically demanding hexasubstituted naphthalenic core. The C5–C13 chiral fragment has been assembled via a stereoselective Johnson orthoester rearrangement of an optically pure allylic alcohol derived from d-glucose. Our studies lay the platform for the determination of the absolute configuration of the unassigned C8-stereocenter of the title compounds in addition to the completion of the total synthesis of the unique ansamacrolides hygrocins A and B.     

Enantioselective Synthesis of L-CCG-I

Introduction of natural menthol as the chiral auxiliary in a gamma-Br-alpha,beta-unsaturated ester leads to enantioselective generation of three chiral centers in a single step on reaction with a glycine anion equivalent to provide L-CCG-I in 94% ee.     

Asymmetric total synthesis of ent-cyclooroidin

An enantiospecific total synthesis of the pyrrole-imidazole natural product cyclooroidin from histidine is described. The key N1-C9 bond is constructed through an intramolecular SN2-type of reaction of a chloro ester. Subsequent imidazole azidation at the 2-position, pyrrole bromination, azide reduction, and deprotection leads to the completion of the synthesis.     

Corrigendum to: Oxidative reactions of tetrahydrobenzimidazole derivatives with N-sulfonyloxaziridines [Tetrahedron Lett. 48 (2007) 5771–5774]

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Studies toward the total synthesis of axinellamine and massadine

Intramolecular Diels-Alder reactions of several N-O linked 4-vinylimidazole dimers provide the expected adduct in moderate to good yield as a single, all trans stereoisomer, along with smaller amounts of the inverse electron demand adduct. Oxidative rearrangement of the cycloadducts occurs on treatment with Davis' reagent, providing a single spiro imidazolone in good yield and with excellent levels of stereocontrol albeit epimeric at the spiro center found in axinellamine and massadine.     

A ring closing metathesis approach to the indole alkaloid mitralactonine

An efficient utilisation of RCM leading to a convenient synthesis of a pentacyclic indole alkaloid is described.     

Total synthesis of nothapodytine B and (±)-mappicine

A novel, efficient total synthesis of the naturally occurring antiviral nothapodytine B (2, mappicine ketone) is reported. The approach is based on the successful implementation of the Johnson orthoester rearrangement of allylic alcohol 7 for assembly of a pyridone D ring precursor with the necessary functionalities. Nothapodytine B is converted into mappicine 3 by NaBH₄ reduction.     

Silver-catalyzed [2,3]-rearrangement of halonium ylides derived from allyl and propargyl halides and alkyl diazoacetates

A silver(I) complex derived from a polyfluorinated tris(pyrazolyl)borate effectively catalyzes carbene transfer to allylic and propargylic halides, leading to the formation of alpha-haloacetate derivatives.     

Total synthesis of 7'-desmethylkealiiquinone

The total synthesis of an analogue of the marine alkaloid kealiiquinone has been completed through application of an intramolecular Diels-Alder reaction of an imidazole-containing enyne. Oxidative aromatization of the lactone adduct and N-methylation facilitates C2-oxidation via the imidazolium salt. Conversion of the lactone to the phthalaldehyde derivative and then to the dihydroxybenzoquinone was achieved via a reaction with glyoxal in the presence of KCN. Esterification of the vinylogous diacid and deprotection provided 7'-desmethylkealiiquinone.     

Oxidative reactions of tetrahydrobenzimidazole derivatives with N-sulfonyloxaziridines

An investigation of the utility of N-sulfonyloxaziridines to effect the oxidative rearrangement of tetrahydrobenzimidazoles to spiro fused 5-imidazolones is reported. In addition to the anticipated rearrangement manifold, it was found that 2-amino substituted derivatives afford products resulting from rearrangement, or alternatively from addition of methanol or water depending on the nature of the N-substituents and reaction conditions.