Carlos Roque Duarte Correia

Substrate-Directable Heck Reactions with Arenediazonium Salts. The Regio- and Stereoselective Arylation of Allylamine Derivatives and Applications in the Synthesis of Naftifine and Abamines

The palladium-catalyzed, substrate-directable Heck-Matsuda reaction of allylamine derivatives with arenediazonium salts is reported. The reaction proceeds under mild conditions, with excellent regio- and stereochemical control as a function of coordinating groups present in the allylamine substrate. The distance between the olefin moiety and the carbonylic system seems to play a key role regarding the regiocontrol. The method presents itself as robust, as simple to carry out, and with wide synthetic scope concerning the allylic substrates and the type of arenediazonium employed. The synthetic potential of the method is illustrated by the short total syntheses of the bioactive compounds naftifine, abamine, and abamine SG.

Intermolecular Enantioselective Heck-matsuda Arylations Of Acyclic Olefins: Application To The Synthesis Of β-aryl-γ-lactones And β-aryl Aldehydes

We describe herein a synthetically useful method for the enantioselective intermolecular Heck-Matsuda arylation of acyclic allylic alcohols. Aryldiazonium tetrafluoroborates were applied as arylating agents in the presence of Pd(TFA)2 and a chiral, commercially available, bisoxazoline ligand. The methodology is straightforward, robust, scalable up to a few grams, and of broad scope allowing the synthesis of a range of β-aryl-carbonyl compounds in good to high enantioselectivities and yields. This new enantioselective Heck-Matsuda arylation allowed the synthesis of β-aryl-γ-lactones and β-aryl aldehydes, which play a vital role as key intermediates in the synthesis of the biologically active compounds, such as (R)-baclofen, (R)-rolipram, (S)-curcumene, (S)-dehydrocurcumene, and (S)-tumerone.

Heck reaction of endocyclic enecarbamates with diazonium salts. Formal enantioselective syntheses of alkaloids (−)-codonopsine and (−)-codonopsinine, and the synthesis of a new C-aryl azasugar

Abstract Formal total syntheses of the pyrrolidine alkaloids (−)-codonopsine and (−)-codonopsinine, as well as the synthesis of a new C-aryl azasugar were accomplished from a common 5-membered, enantiomerically pure endocyclic enecarbamate. The key step in those syntheses relies on a novel and practical version of the Heck reaction involving endocyclic enecarbamates and diazonium salts.

Coumarins from Free ortho-Hydroxy Cinnamates by Heck-Matsuda Arylations: A Scalable Total Synthesis of (R)-Tolterodine

Free ortho-hydroxy cinnamate ester derivatives are evaluated in the synthesis of structurally diverse 4-aryl-coumarins via a tandem Heck-Matsuda cyclization reaction. Free phenolic groups were considered incompatible with such a reaction, which usually provide the corresponding diazo dyes. A concise and scalable route employing a ligand-free, Pd-catalyzed Heck-Matsuda arylation under aerobic conditions for the preparation of (R)-Tolterodine in high overall yield and ee is also presented.

Highly Regio- and Stereoselective Heck Reaction of Allylic Esters with Arenediazonium Salts: Application to the Synthesis of Kavalactones

A highly efficient palladium-catalyzed Heck reaction of allylic esters with arenediazonium salts is described. The reaction proceeds under mild conditions, with excellent to total regio- and stereochemical control and with retention of the traditional leaving group. Furthermore, the generality of the present methodology is illustrated by the short total synthesis of the natural kavalactones, yangonine, (+/-)-methysticin, and (+/-)-dihydromethysticin.

Differential oxidation of endocyclic enecarbamates. Synthesis of cyclic β-hydroxy-α-amino acids

Abstract The differential oxidation of five and six-membered endocyclic enecarbamates was investigated employing m -CPBA, DMD, as well as enantioselective protocols such as the Kochi-Jacobsen-Katsukis epoxidation and the Sharpless dihydroxylation. By this strategy the syntheses of β-hydroxyprolines and β-hydroxypipecolic acids were accomplished. X-Ray crystallographic analysis of the trans -β-hydroxypipecolic acid was instrumental to solve structural assignment conflicts.

Synthesis of dihydroxylated prolines and iminocyclitols from five-membered endocyclic enecarbamates. Total synthesis of the potent glycosidase inhibitor (2R,3R,4R,5R)-2,5-dihydroxymethyl-3,4-dihydroxypyrrolidine (DMDP)

cis- and trans-3,4-Dihydroxylated prolines and the iminocyclitol 1,4-dideoxy-1,4-imino ribitol were synthesized employing a strategy involving the Heck arylation of five-membered endocyclic enecarbamates with aryldiazonium salts followed by oxidative cleavage of the electron-rich aromatic ring. The total synthesis of the potent α- and β-glucosidase inhibitor (2R,3R,4R,5R)-2,5-hydroxymethyl-3,4-dihydroxypyrrolidine (DMDP) was also achieved by the same strategy in ten steps from a chiral five-membered enecarbamate in 12% overall yield.

Quaternary Stereogenic Centers through Enantioselective Heck Arylation of Acyclic Olefins with Aryldiazonium Salts: Application in a Concise Synthesis of (R)-Verapamil

We describe herein a highly regio- and enantioselective Pd-catalyzed Heck arylation of unactivated trisubstituted acyclic olefins to provide all-carbon quaternary stereogenic centers. Chiral N,N ligands of the pyrimidine- and pyrazino-oxazoline class were developed for that purpose, providing the desired products in good to high yields with enantiomeric ratios up to >99:1. Both linear and branched substituents on the olefins were well-tolerated. The potential of this new method is demonstrated by the straightforward synthesis of several O-methyl lactols and lactones containing quaternary stereocenters, together with a concise enantioselective total synthesis of the calcium channel blocker verapamil.

Heck arylations of N-acyl-3-pyrroline and N-acyl-1,2,5,6-tetrahydropyridine with aryldiazonium salts. Short syntheses of aryl γ- and δ-lactams, baclofen, homobaclofen and analogues

Heck arylation of N-acyl-3-pyrrolines and an N-acyl-tetrahydropyridine with aryldiazonium tetrafluoroborates under phosphine-free conditions proceeded smoothly to give α-hydroxycarbamates (hemiaminals) or α-alkoxycarbamates which were oxidized to the desired γ- and δ-lactams. Acidic hydrolysis of the γ-lactams produced a series of arylated GABA derivatives, including baclofen, a useful therapeutic drug, in only three steps with an overall yield of 63–76%. Starting from N-acyl-tetrahydropyridine, aryl-δ-lactams and higher homologues of baclofen can be obtained.

STEREOSELECTIVE SYNTHESIS OF CONFORMATIONALLY RESTRICTED ANALOGUES OF ASPARTIC AND GLUTAMIC ACIDS FROM ENDOCYCLIC ENECARBAMATES

Abstract The stereoselective synthesis of cyclic amino acids incorporating the core framework of aspartic acid and glutamic acids were accomplished from a common intermediate. Oxidative cleavage of an aza-bicyclic-dichlorocyclobutanone/pentanone with Me 2 CuLi Ac 2 O followed by ozonolysis furnished the amino acid derivatives in good overall yields in a three-step sequence. This protocol was also applied to the synthesis of a cis - β -amino acid and to the enantioselective construction of a chimeric amino acid incorporating the basic skeleton of four different naturally occurring amino acids into a single structure.