ABSTRACT
A concise formal synthesis of echinopines A and B is reported. The key [5.5.7] tricyclic intermediate, which has been previously used for the synthesis of echinopine A and B, was assembled using Cr(0)-promoted photochemical [6π + 2π] cycloaddition followed by a radical cyclization step.
Subject(s)
Sesquiterpenes/chemical synthesis , Cyclization , Cycloaddition Reaction , Echinops Plant/chemistry , Molecular Structure , Plant Roots/chemistry , Sesquiterpenes/chemistryABSTRACT
A common strategy for the stereoselective and protecting group-free total synthesis of the myxobacterial antibiotics myxothiazole Z, (14S)-melithiazole G and (14S)-cystothiazole F is described featuring an asymmetric organocatalytic transfer hydrogenation, a palladium-catalyzed Stille coupling and a cross-metathesis as the key steps.
Subject(s)
Anti-Bacterial Agents/chemical synthesis , Thiazoles/chemical synthesis , Anti-Bacterial Agents/chemistry , Catalysis , Hydrogenation , Palladium/chemistry , Stereoisomerism , Thiazoles/chemistryABSTRACT
A convergent synthesis of the C1-C11 and C12-C34 fragments of mycalolide A is described. Synthetic highlights include a highly E-selective cross-metathesis between a vinyl-functionalized bis-oxazole unit and a polypropionate side chain to introduce the C19-C20 double bond and an enzymatic desymmetrization of a meso-diol in addition to five stereoselective allylations/crotylations to control the 11 stereogenic centers present in the natural product.
Subject(s)
Macrolides/chemical synthesis , Oxazoles/chemical synthesis , Animals , Macrolides/chemistry , Marine Toxins , Molecular Structure , Oxazoles/chemistry , Porifera/chemistry , StereoisomerismABSTRACT
Beta-azole-containing alpha,beta-unsaturated aldehydes were successfully reduced under highly enantioselective organocatalytic transfer hydrogenation conditions. The products were obtained in good yields and up to 94% optical purity. This simple process was successfully applied to the synthesis of the C7-C14 fragment of ulapualide A, a natural product which exhibits promising antitumor activity.
ABSTRACT
Photoinitiated [6pi + 2pi] cycloadditions of allenes with (eta(6)-cycloheptatriene)tricarbonylchromium(0) (1) are described. An example of asymmetric induction obtained by reaction of 1 with a chiral 1,3-disubstituted allene is also reported.
Subject(s)
Alkadienes/chemical synthesis , Chromium/chemistry , Organometallic Compounds/chemistry , Alkadienes/chemistry , Cyclization , Photochemical ProcessesABSTRACT
A ruthenium-based catalyzed olefin cross-methathesis reaction involving 2- and 4-vinyl-functionalized oxazoles was developed. A wide range of olefinic partners was coupled in good to excellent yields and high stereoselectivities under mild conditions. This methodology offers new opportunities for the synthesis of a plethora of biologically active natural products.
Subject(s)
Oxazoles/chemical synthesis , Vinyl Compounds/chemical synthesis , Catalysis , Organometallic Compounds/chemistry , Ruthenium/chemistry , Vinyl Compounds/chemistryABSTRACT
[structure: see text]. A total synthesis of acetylcholine blocking agent, phenserine, has been achieved by employing a [4+1] cyclization between an appropriately substituted indole isocyanate and a bis(alkylthio)carbene.
Subject(s)
Indoles/chemistry , Isocyanates/chemistry , Methane/analogs & derivatives , Physostigmine/analogs & derivatives , Sulfides/chemistry , Cyclization , Hydrocarbons/chemistry , Methane/chemistry , Molecular Structure , Physostigmine/chemical synthesis , Physostigmine/chemistry , Physostigmine/pharmacologyABSTRACT
[reaction: see text] Highly substituted beta-lactams have been isolated as the major product of the reaction of dimethoxycarbene with selected isocyanates. This reaction offers the potential for rapid access into a variety of highly functionalized species.
Subject(s)
Isocyanates/chemistry , Methane/analogs & derivatives , beta-Lactams/chemical synthesis , Hydrocarbons/chemistry , Methane/chemistry , Molecular StructureABSTRACT
An efficient protecting group controlled regioselective chromium(0)-mediated three-component higher order cycloaddition of tethered diynes with cyclic trienes that generates five rings and six stereogenic centers in one step is described. Following a sequence of reactions featuring a chemoselective Baeyer-Villiger rearrangement and a regioselective cyclopropane hydrogenolysis, the total synthesis of 9-epi-pentalenic acid was achieved.
Subject(s)
Chromium/chemistry , Sesquiterpenes/chemical synthesis , Models, Chemical , Molecular Conformation , Molecular StructureABSTRACT
[reaction: see text] The rapid construction of highly substituted 4-aminopyridones was achieved employing an efficient cyclization between various vinyl isocyanates and 2-methylene dihydrobenzimidazole.
ABSTRACT
[reaction: see text] Vinyl ketenes have been shown to undergo [4 + 1] cycloaddition with a variety of nucleophilic carbenes to deliver highly substituted cyclopentenones as products.
ABSTRACT
[reaction: see text] N-Heterocyclic carbenes have been found to undergo [4 + 1] cycloaddition with various vinyl isocyanates to afford functionalized hydroindolone products.
ABSTRACT
The scope of solid-phase reactions utilizing a 'traceless' pi-arene-chromium linker has been expanded to include the addition of organo-lithium reagents to a supported ester group, generation and alkylation of an enolate anion, and substitution via the Mitsunobu reaction. Immobilization of ortho-disubstituted polyfunctionalized arene chromium dicarbonyl species onto the solid support and subsequent, selective transformation is also reported.
Subject(s)
Benzene Derivatives/chemistry , Chromium/chemistry , Cross-Linking Reagents/chemistry , Organometallic Compounds/chemistry , Anions , Combinatorial Chemistry Techniques , Esters , Lithium/chemistry , Polystyrenes/chemistry , Styrene/chemistryABSTRACT
[reaction: see text] The efficient construction of an ingenol intermediate exhibiting "insideminus signoutside" intrabridgehead stereochemistry is reported. The sequence features the net conversion of a cis-intrabridgehead compound into a highly strained trans-species via palladium-mediated isomerization of an allylic epoxide followed by a low-temperature alkoxide-accelerated 1,5-hydrogen migration.
