Total synthesis of (+)-phomactin a using a B-alkyl Suzuki macrocyclization

A total synthesis of (+)-phomactin A is described using a B-alkyl Suzuki macrocyclization to incorporate the isolated trisubstituted olefin. This macrocyclization was accomplished with the sensitive hydrated furan ring in place. (R)-(+)-pulegone was used to establish the highly substituted cyclohexene core of the molecule.     

Asymmetric synthesis of (-)-indolizidine 209D via B-alkyl Suzuki coupling and amination reactions

(-)-Indolizidine 209D has been synthesized using consecutive amination reactions of compound 11. The precursor was prepared concisely using B-alkyl Suzuki cross coupling of chiral homoallyl amine and vinyl iodide compounds. Reaction: see text.     

Regulation of cyclization for the stereoselective synthesis of substituted tetrahydrofurans and tetrahydrooxepines

Dramatic solvent effect is observed during the cyclization of 1. Synthesis of 2 is achieved from the reaction of 1 with a hexamethylditin-catalyzed palladium complex followed by aldehydes in the presence of TMSOTf in THF, whereas 3 is formed in CH2Cl2. The method described herein is successful with various substrates 1 in good yields and high levels of diastereoselectivity.     

Application of the B-alkyl suzuki-miyaura cross-coupling reaction to the stereoselective synthesis of analogues of (3S)-oxidosqualene

[reaction: see text] A general method is described for the direct and stereoselective synthesis of epoxypolyenes via Suzuki-Miyaura cross-coupling reaction of 1-iodoalkenes with B-alkylboron compounds. It allows for the straightforward and convergent assembly of compounds that are structurally similar to (3S)-oxidosqualene, an important intermediate in steroid biosynthesis.     

A stereoselective intramolecular 1,3-dipolar nitrone cycloaddition for the synthesis of substituted chromanes

A stereoselective intramolecular 1,3-dipolar nitrone cycloaddition useful in the synthesis of chromanes is described. The reaction relies on the use of a chiral auxiliary on the nitrone partner. Key to the success of the reaction is the choice of auxiliary and the choice of Lewis acid catalyst. Utilizing an auxiliary with a pendant coordinating group, and Zn(OTf)(2) as the Lewis acid, diastereoselectivities up to 22:1 could be achieved.     

Allene-alkyne cross-coupling for stereoselective synthesis of substituted 1,4-dienes and cross-conjugated trienes

Titanium-mediated cross-coupling of allenic alcohols with alkynes has been investigated. Divergent reaction pathways were discovered that provide either stereodefined 1,4-dienes or substituted cross-conjugated trienes. In short, allene substitution plays a critical role in the determination of reaction pathway.     

Allene-alkyne cross-coupling for stereoselective synthesis of substituted 1,4-dienes and cross-conjugated trienes

Titanium-mediated cross-coupling of allenic alcohols with alkynes has been investigated. Divergent reaction pathways were discovered that provide either stereodefined 1,4-dienes or substituted cross-conjugated trienes. In short, allene substitution plays a critical role in the determination of reaction pathway.     

Double intramolecular oxymercuration: stereoselective synthesis of highly substituted bis-tetrahydrofuran

Stereoselective intramolecular oxymercuration has been demonstrated as the key reaction for the efficient preparation of mono- and dihydroxylated unsymmetrical bis-tetrahydrofuran skeletons present in naturally occurring biologically active acetogenins using carbohydrates. These trans- and syn-selective intramolecular oxymercurations were explored in an enantioselective synthesis of the bis-tetrahydrofuran skeleton of mucoxin.     

Enantioselective synthesis of substituted pyrans via amine-catalyzed Michael addition and subsequent enolization/cyclisation

An organocatalytic construction of optically enriched substituted pyran derivatives via amine-catalyzed Michael addition and subsequent enolization/cyclisation has been described starting from electronically poor alkenes. Functionalized pyrans were obtained in high enantioselectivities (up to 96%) and good yields (up to 90%) having three contiguous chiral centers.     

Iminium ion cyclizations. Highly stereoselective synthesis of substituted tetrahydroisoquinoline derivatives

Cationic cyclizations of acyliminium ions $\text{2}$ (R₁  phenyl) occur with high stereo-selectivity, which is suggested to originate in the intermediate arenium ions.     

A stereoselective synthesis of asymmetrically substituted calix[4]arenecarbamates

Calix[4]arenes bearing a methoxy and an R or S α-phenylethylacetamido group at the narrow rim of macrocycles are stereoselectively acylated with 1 equiv of trichloroacetyl isocyanate to give chiral asymmetrically substituted calix[4]arenecarbamates in preparative yields and high diastereomeric excess.     

Resonance capture of electrons by molecules of substituted pyrans

Negative-ion mass spectrometry in the mode of resonance capture of electrons and photoelectron spectroscopy in combination with quantum-chemical calculations showed that the formation of the resonance states of negative molecular ions in the reaction of electrons with molecules of the mechanism of intershell Feshbach resonance with the consecutive excitation of an electron from several higher occupied MO to one vacant MO. In a low-energy region, the resonance at 1.4 eV is a resonance of form and the resonance at 3–4 eV is the usual electron exciting Feshbach resonance with a parent triplet state (π.π*)³. The one and the same vacant π*_CC MO is “active” in all the resonances mentioned. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1892–1894, October, 1997.     

Palladium-containing perovskites: recoverable and reuseable catalysts for Suzuki couplings

Palladium-containing perovskites (LaFe0.57Co0.38Pd0.05O3) have been exploited as recoverable and reuseable catalysts in Suzuki coupling reactions; residual levels of Pd after removal of the catalyst by filtration are low (2 ppm) despite evidence that the reaction is occurring via a homogeneous process.     

Iodine assisted modified Suzuki type reaction of bicyclic hydrazines: stereoselective synthesis of functionalized cyclopentenes

Bicyclic hydrazines undergo a facile palladium/iodine mediated stereoselective ring opening on reaction with organoboronic acids affording trans-3,4-disubstituted hydrazino cyclopentenes in good to excellent yield.     

Total synthesis of (+)-(2'S,3'R)-zoapatanol exploiting the B-alkyl Suzuki reaction and the nucleophilic potential of the sulfinyl group

A stereoselective synthesis of the diterpenoid oxepane (+)-zoapatanol is described. The key steps include a B-alkyl Suzuki cross-coupling reaction for the stereoselective synthesis of trisubstituted alkenes, creation of the two stereogenic centers on the oxepane ring by heterofunctionalization of an alkene through substrate control exploiting the nucleophilic potential of an intramolecular sulfinyl group, and transformation of a β-hydroxy sulfoxide into a terminal alkene.     

Straightforward one-pot stereoselective synthesis of substituted tetrahydrofurans from 1,3-butadienes and aldehydes

A new and efficient multicomponent reaction involving a double-allylation sequence is reported. In situ generated bimetallic reagents are prepared from disilane 1 and added onto a range of aliphatic aldehydes to afford a direct access to trisubstituted tetrahydrofurans in good to excellent diastereoselectivity (up to 70%).     

Flow reactor synthesis of unsymmetrically substituted p-terphenyls using sequentially selective Suzuki cross-coupling protocols

ABSTRACT

Synthetic procedures, based on integrated flow chemical methods, have been developed for the sequential chemo-selective Suzuki–Miyaura cross-coupling of 1,4-dibromo-2-nitrobenzene (1) with various arylboronic acids. The first Suzuki coupling step used a phosphine-(ligand)-free palladium catalyst at room temperature and gave regio-selective coupling of (1) at the ortho-position to the nitro group. The bromo-biaryl product was then directly subjected in situ to a second coupling step, using different arylboronic acids, as a continuous in-flow operation. Based on this methodology, a number of unsymmetrically substituted p-terphenyl compounds were synthesized in excellent overall yields. This approach provides a convenient route to this class of compounds, and is suited for the generation of targeted chemical libraries, or the synthesis of precursors of biologically active natural product analogues that contain the p-terphenyl core. During the first coupling step, dimerization at low levels of the bromo-biaryl intermediate occurred, leading to formation of quaterphenyl compounds.