A Metal-Free Tandem C–C/C–O Bond Formation Approach to Diversely Functionalized Tetrasubstituted Furans

A novel and efficient method for the synthesis of diversely functionalized furans is developed via DBU-mediated tandem Michael addition/5-<i>exo-dig</i>-cycloisomerization of enynes and keto-methylenes. This [3 + 2]-annulation is operationally simple under metal-free reaction conditions with 100% atom economy and broad substrate scope

Proline-threonine dipeptide as an organocatalyst for the direct asymmetric aldol reaction

A new proline-threonine (H-Pro-Thr-OH) dipeptide has been demonstrated as an efficient organocatalyst for a direct asymmetric aldol reaction. It was found that this new peptide-based catalyst efficiently catalyzed the reaction between an aldehyde and acetone to provide β-hydroxy ketones in good yields with good enantioselectivities

Stereoselective synthesis of tetrahydropyranyl diarylheptanoids (−)-centrolobine and (+)-centrolobine

A versatile chiron approach to the tetrahydropyranyl diarylheptanoid natural products (−)-centrolobine and (+)-centrolobine has been described. The use of an aldol reaction followed by reductive etherification for the formation of tetrahydropyran ring is of importance

Novel [4 + 2]-Benzannulation To Access Substituted Benzenes and Polycyclic Aromatic and Benzene-Fused Heteroaromatic Compounds

A common [4 + 2]-benzannulation of Morita–Baylis–Hillman acetates of acetylenic aldehydes with boronic acids has been developed for the synthesis of aromatic and heteroaromatic compounds through tandem allylic substitution/hydroarylative cycloisomerization process. This method provides a facile and general route to substituted benzenes, naphthalenes, other polycyclic aromatics, and various benzene-fused heteroaromatic compounds such as benzofuran, benzothiophene, indole, and carbazoles

Domino alkyne insertion/aldol reaction/aromatization of 2-alkynyl indole-3-carbaldehyde with 1,3-diketones: entry to 2-indolyl phenols

International audienceA novel one-pot base-promoted insertion of indolyl 2-alkynes into a C-C single bond of 1,3-diketones, followed by intramolecular aldol reaction and dehydrative aromatization is described. This reaction cascade leads to the construction of 2-indolyl phenols involving the formation of the C1-C2 and C3-C4 bonds of phenols resulting from the formal insertion process with a good substrate scope. Further, these bifunctional compounds were used in a novel arylative annulation in the presence of Grignard reagents to provide chromeno-indole frameworks

A Thioannulation Approach to Substituted Thiophenes from Morita–Baylis–Hillman Acetates of Acetylenic Aldehydes

A new protocol has been developed for the synthesis of substituted thiophenes under mild and metal-free reaction conditions via the base-promoted thioannulation of Morita–Baylis–Hillman acetates of acetylenic aldehydes with potassium thioacetate involving a tandem allylic substitution/deacetylative 5-exo-<i>dig</i>-thiocycloisomerization. The obtained products provide an entry to 4<i>H</i>-thieno­[3,2-<i>c</i>]­chromene and thieno­[3,2-<i>c</i>]­dihydroquinoline

Aza-Annulation of Enynyl Azides: A New Approach to Substituted Pyridines

Synthesis of substituted pyridines through a novel aza-annulation of 2-en-4-ynyl azides, derived from MBH-acetates of acetylenic aldehydes, is described. A variety of enynyl azides having aryl, heteroaryl, and alkyl groups on the alkyne functionality successfully participated in the Ag-mediated annulation reaction to provide the corresponding 3,6-disubstituted pyridines. I₂-Mediated cyclization was found to be controlled by the substituent on the alkyne functionality, which offered the 5-iodo-3,6-disubstituted pyridines from enynyl azides having an electron-rich substituent on the alkyne functionality