Palladium(0)-catalyzed arylative dearomatization of phenols

The palladium-catalyzed arylative dearomatization of phenols to yield spirocyclohexadienone products in good to excellent yields has been developed. Preliminary results demonstrate that the formation of the spirocyclic all-carbon quaternary center can be accomplished with high levels of enantiocontrol (up to 91% ee).

Formation of ArF from LPdAr(F): catalytic conversion of aryl triflates to aryl fluorides

Despite increasing pharmaceutical importance, fluorinated aromatic organic molecules remain difficult to synthesize. Present methods require either harsh reaction conditions or highly specialized reagents, making the preparation of complex fluoroarenes challenging. Thus, the development of general methods for their preparation that overcome the limitations of those techniques currently in use is of great interest. We have prepared [LPd(II)Ar(F)] complexes, where L is a biaryl monophosphine ligand and Ar is an aryl group, and identified conditions under which reductive elimination occurs to form an Ar-F bond. On the basis of these results, we have developed a catalytic process that converts aryl bromides and aryl triflates into the corresponding fluorinated arenes by using simple fluoride salts. We expect this method to allow the introduction of fluorine atoms into advanced, highly functionalized intermediates.

Palladium-catalyzed asymmetric dearomatization of naphthalene derivatives

An intramolecular enantioselective metal-catalyzed dearomatization reaction is described. This procedure allows the dearomatization of naphthalene derivatives through an electrophilic aromatic substitution-type reaction on a Pd(II) intermediate. The high yields and enantioselectivities achieved make this procedure a valuable method for synthetic chemists.

Twofold C-H functionalization: palladium-catalyzed ortho arylation of anilides

The ortho arylation of anilides to form biphenyls via a twofold C-H functionalization/C-C bond-forming process is described. The oxidative coupling takes place in the presence of 5-10 mol % of Pd(OAc)2, 10-20 mol % of DMSO, and 4-11 equiv of the aryl substrate in TFA under an oxygen atmosphere. No metal-containing cocatalyst is required.

The total synthesis and biological properties of the cytotoxic macrolide FD-891 and its non-natural (Z)-C12 isomer

A total, stereoselective synthesis of the naturally occurring, cytotoxic macrolide FD-891 and of its non-natural (Z)-C12 isomer is described. Three fragments of the main carbon chain were stereoselectively prepared by using asymmetric aldol and allylation reactions as the key steps. The molecule was then assembled by using two Julia-Kocienski olefinations to connect the three fragments and a Yamaguchi reaction to close the macrolactone ring. Some specific biological properties (cytotoxicity, binding to tubulin) have been determined for both macrolides. The E configuration of the C12-C13 olefinic bond seems to be an important feature in determining the cytotoxicity but the precise biological mechanism of the latter still remains to be cleared.

Stereoselective synthesis of the cytotoxic macrolide FD-891

[reaction: see text] A total synthesis of the naturally occurring, cytotoxic macrolide FD-891 is described. Three fragments were first stereoselectively constructed using mainly asymmetric aldol and allylation reactions. The complete framework was then assembled using two Julia-Kocienski olefinations to connect the three fragments and a Yamaguchi reaction to close the macrolactone ring.

An efficient, asymmetric organocatalyst-mediated conjugate addition of nitroalkanes to unsaturated cyclic and acyclic ketones

5-Pyrrolidin-2-yltetrazole is a versatile organocatalyst for the asymmetric conjugate addition of nitroalkanes to enones. Using this catalyst, this transformation requires short reaction times, tolerates a broad substrate scope, and possibly proceeds via generation of an iminium species.

Stereoselective Total Synthesis and Absolute Configuration of the Natural Decanolides (−)-Microcarpalide and (+)-Lethaloxin. Identity of (+)-Lethaloxin and (+)-Pinolidoxin

[reaction: see text] Convergent, stereoselective syntheses of the pharmacologically active, naturally occurring lactones (-)-microcarpalide and (+)-lethaloxin have been achieved from the commercially available, chiral reagents (R)-glycidol, (S,S)-tartaric acid, and d-ribose as the starting materials. These syntheses have further served to establish the hitherto unknown absolute configuration of (+)-lethaloxin and to show its identity with (+)-pinolidoxin.

Synthesis and Complete Stereochemical Assignment of Psymberin/Irciniastatin A

We describe a concise and flexible synthetic avenue for the preparation of compounds with structures relevant to those proposed for the novel marine-derived differential cytotoxins psymberin and irciniastatin A. Our efforts led to their complete stereochemical assignment and the notion that psymberin and irciniastatin A are identical compounds. Our total synthesis features an interesting termini-differentiating lactolization of a dialdehyde obtained from a C2-symmetrical bis-olefin precursor, a mild platinum-catalyzed hydrolysis of an epimerizable nitrile, a novel protocol to prepare sensitive methyl imidates, and a one-pot conversion of these imidates to N-acyl aminals. Starting from fragments 5-7 (prepared in 7-8 steps each, 30-49% overall yield) the synthesis of psymberin/irciniastatin A was completed in an additional 9 steps and 30% yield (17 steps longest linear sequence, 8.9% overall).

A Photochemical Entry to Depsides: Synthesis of Gustastatin

Herein, we propose a modular and general strategy to construct orcinol-type depsides based on the photolysis of functionalized benzodioxinones (I). Notably, resorcinylic esters are obtained without competing isocoumarin (II) formation, exemplified by the first total synthesis of gustastatin in 10 steps from commercially available trihydroxybenzoic acid. [Structure: see text]

Stereoselective Synthesis of the Antiprotozoal Lactone Passifloricin A and Seven Isomers Thereof

The conjugated delta-lactone passifloricin A, a natural product with antiprotozoal activity, and seven isomers thereof have been synthesized in enantiopure form. It has been shown in this way that the proposed structure for the natural compound was erroneous. The correct structure is now evidenced. Key steps of the syntheses were asymmetric Brown-type aldehyde allylations and ring-closing metatheses.

On the structure of passifloricin A: asymmetric synthesis of the delta-lactones of (2Z,5S,7R,9S,11S)- and (2Z,5R,7R,9S,11S)tetrahydroxyhexacos-2-enoic acid

Stereoselective syntheses of the delta-lactone of (2Z,5S,7R,9S,11S)-tetrahydroxyhexacos-2-enoic acid, the structure reported for passifloricin A, and of its (5R)-epimer are described. The creation of all stereogenic centers relied upon Brown's asymmetric allylation methodology. The lactone ring was created via ring-closing metathesis. The NMR data of both synthetic products, however, were different from those of the natural product. The published structure of passifloricin A is thus erroneous and will require further synthetic work to be unambiguously assigned. [structure: see text]

Stereoselective synthesis of microcarpalide

The first total synthesis of the naturally occurring nonenolide, microcarpalide, is described. The key step in the synthesis was the ring-closing metathesis of a dienic ester prepared in turn by coupling an acid and an alcohol stereoselectively synthesized from (S,S)-tartaric acid and (R)-glycidol, respectively. [structure: see text]