Reaction of α-amino acids, particularly prolines and their derivatives with carbonyl compounds via decarboxylative redox process, is a viable strategy for synthesis of structurally diverse nitrogen centered heterocyclics. In these processes, the decarboxylation is the essential driving force for the processes. The realization of the redox process without decarboxylation may offer an opportunity to explore new reactions. Herein, we report the discovery of an unprecedented redox Claisen-type condensation aromatization cascade reaction of 4-substituted 4-hydroxyproline and its esters with unreactive ketones. We found that the use of propionic acid as a catalyst and a co-solvent can change the reaction course. The commonly observed redox decarboxylation and aldol condensation reactions are significantly minimized. Moreover, unreactive ketones can effectively participate in the Claisen condensation reaction. The new reactivity enables a redox cyclization via an unconventional Claisen-type condensation reaction of in situ formed enamine intermediates from ketone precursors with 4-substituted 4-hydroxyproline and its esters as electrophilic acylation partners. Under the reaction conditions, the cascade process proceeds highly regio- and stereoselectively to afford highly synthetically and biologically valued cis-2,3-dihydro-1H-pyrrolizin-1-ones with a broad substrate scope in efficient ‘one-pot’ operation, whereas such structures generally require multiple steps.

A Pd-catalyzed, site-selective p-hydroxyphenyloxylation of benzylic α-C(sp3)–H bonds with 1,4-benzoquinone using thioamide as a directing group is reported. 1,4-Benzoquinone is employed as the p-hydroxyphenyloxy source without extra oxidants. This method exclusively gives site selectivity at α-C(sp3)–H bonds rather than the usual β-C(sp3)–H bonds through C–H activation mode. The reactions proceed with high functional group tolerance in yields of 42–93%.

A novel one-pot efficient synthesis of 2,5-dihydro-1H-benzo[c]azepines and 10,11-dihydro-5H-benzo[e]pyrrolo[1,2-a]azepines from α-amino acids and aromatic aldehydes containing an ortho-Michael acceptor is reported via decarboxylative annulations without metal catalysts in yields of 52–91%. Under microwave irradiation, this protocol provides rapid access to polycyclic ring systems (only 5 min in most cases).

We report a novel organocatalytic one-pot cascade bromination–Michael-type Friedel–Crafts alkylation dearomatization–nucleophilic rearrangement aromatization cascade process for the direct α-indolylation of unfunctionalized enals from readily available indoles with good yields and high E selectivity. The simplicity and practicality of its high efficiency for formation of a new C(sp2)–C(sp2) bond constitute the most attractive advantage of this reaction.

An unprecedented acetic acid-catalyzed efficient access to N-alkylpyrroles from reaction of 4-hydroxy-l-proline with a variety of aldehydes has been achieved in good to excellent yields under mild reaction conditions.

A mild and highly efficient amine-catalyzed, IBX-mediated oxidation of aldehydes to (E) selective α,β-unsaturated aldehydes has been achieved in good yields. The process features a new oxidation of enamines to iminium ions in a catalytic fashion.

We report a novel organocatalytic one-pot cascade bromination–Michael-type Friedel–Crafts alkylation dearomatization–nucleophilic rearrangement aromatization cascade process for the direct α-indolylation of unfunctionalized enals from readily available indoles with good yields and high E selectivity. The simplicity and practicality of its high efficiency for formation of a new C(sp2)–C(sp2) bond constitute the most attractive advantage of this reaction.