A cobalt complex of a microbial arene oxidation product

ABSTRACT: We report the first synthesis of a cobalt Cp diene complex wherein the diene is derived by microbial dearomatising dihydroxylation of an aromatic ring. The complex has been characterised crystallographically and its structure is compared to that of an uncomplexed diene precursor.     

Photooxygenation of a microbial arene oxidation product and regioselective Kornblum-DeLaMare rearrangement: total synthesis of zeylenols and zeylenones

We report the enantioselective total syntheses of zeylenol (+)-1, as well as its congeners (-)-7 and 16, and of 3-O-debenzoylzeylenone 28. To this end, a new variant of the Kornblum-DeLaMare rearrangement, which utilises neighbouring-group participation to impart regioselectivity, has been developed. The approach employs photooxygenation of building blocks derived from a microbial arene oxidation product.     

Total synthesis and stereochemical assignment of the spiroisoxazoline natural product (+)-calafianin

[STRUCTURE: SEE TEXT] Synthesis of the spiroisoxazoline natural product (+)-calafianin is reported using asymmetric nucleophilic epoxidation and nitrile oxide cycloaddition as key steps. Synthesis and spectral analysis of all calafianin stereoisomers led to unambiguous assignment of relative and absolute stereochemistry.     

Total synthesis of (+)-epiquinamide

The stereoselective total synthesis of the novel quinolizidine alkaloid (+)-epiquinamide is presented, starting from the amino acid l-allysine ethylene acetal. Key steps in the synthesis involved a highly diastereoselective N-acyliminium ion allylation and a ring-closing metathesis reaction to provide the bicyclic skeleton. [reaction: see text]     

Total synthesis of (+)-anamarine

An enantiospecific total synthesis of polyhydroxy δ-pyrone natural product (+)-anamarine is accomplished. The main features of the synthesis include the stereoselective reduction of the ketone obtained by the desymmetrization of the bis-dimethyl amide of tartaric acid and further elaboration involving asymmetric Brown's allylation and ring closing metathesis.     

Total synthesis of (+)-pseudohygroline

A simple and efficient total synthesis of five-membered pyrrolidine, (+)-pseudohygroline is described. The key steps involved in this synthesis are highly stereoselective Prins cyclisation followed by reductive ring opening and hydroboration.     

Total synthesis of (+)-obtusenyne

The stereoselective total synthesis of (+)-obtusenyne is described. The oxonene skeleton possessing trans-orientated alkyl substituents at the α,α′-positions was stereoselectively constructed via cyclization of the corresponding hydroxy epoxide promoted by Eu(fod)₃.     

Total synthesis of (+)-kalkitoxin

The neurotoxic lipopeptide (+)-kalkitoxin was synthesized by a route which employed asymmetric organocopper conjugate addition followed by in situ enolate alkylation to install the anti,anti-1,2,4-trimethyl relationship of the toxin; the synthesis of kalkitoxin required sixteen steps and proceeded in 3% overall yield.     

Total synthesis of (+)-pinitol

A new synthesis of (+)-pinitol 9 has been developed starting from the 7-oxanorbornenic sulfone (+)-5, prepared in enantiomerically pure form by resolution of the sulfonyl-7-oxanorbornanol 4. These precursors are available from the Diels-Alder adduct of furan and trans-1,2-bis-(phenylsulfonyl)-ethylene.     

Total synthesis of (+)-dihydromevinolin

The potent hypocholesterolemic agent (+)-dihydromevinolin was synthesized from chiral pyranoside 5 and octahydronaphthalene 6 which was obtained from maleic anhydride Diels-Alder adduct 7 by intramolecular sulfoxide acylation and methyl cuprate addition.     

Total synthesis of (+)-dactylolide

[reaction: see text] The total synthesis of the new cytotoxic marine macrolide (+)-dactylolide (1) has been achieved in nine steps from known vinyl bromide (-)-AB. In addition, (+)-zampanolide (2) has been converted to (+)-dactylolide (1) via thermolysis.     

Total synthesis of (+)-tedanolide

A convergent, stereocontrolled total synthesis of (+)-tedanolide (1), an architecturally complex marine antitumor macrolide, has been achieved in 31 steps (longest linear sequence). Highlights of the synthesis comprise a highly efficient dithiane union, followed by an Evans-Tishchenko "oxidation" to enable formation of the seco-ester in the presence of an oxidatively labile dithiane, a highly refined protecting group strategy, and a chemo- and stereoselective epoxidation at C(18,19).     

Total synthesis of (+)-asperazine

The first total synthesis of the structurally novel cyclotryptophan alkaloid asperazine is reported. The central step in the synthetic sequence is a diastereoselective intramolecular Heck reaction in which the substituent controlling stereoselection is external to the ring being formed. This synthesis confirmed the structure of (+)-asperazine (1) proposed by Crews and co-workers and provided material for additional biological studies. The in vitro cytotoxicity originally reported for the marine isolate was not confirmed with synthetic (+)-asperazine.     

Total synthesis of (+)-sundiversifolide

The first, enantiocontrolled total synthesis of (+)-sundiversifolide has been accomplished using the sequential ring-closing metathesis, [3,3]-sigmatropic rearrangement, and iodolactonization for the key assembly of the cis-fused oxabicyclo[5.3.0]decene framework of the natural product. [structure: see text]     

Total synthesis of (+)-davidiin

Quite strained: The total synthesis of (+)-davidiin, an ellagitannin with more substituents in axial than in equatorial positions, requires a conformational lock of the glucose, induced by steric repulsion between adjacent bulky silyloxy groups. This conformational lock played a pivotal role in 1)?the β-selective formation of the glycosyl ester at the anomeric position, 2)?the formation of the 1,6-HHDP bridge, and 3)?the complete control of axial chirality in the aryl-aryl coupling.