Wittig homologation of 2-(chloromethyl)-2H-chromen-2-ol derivatives: a new facile synthesis of substituted 2,3-dihydrobenzoxepine-4-carboxylates

Room-Temperature Cascade Electrophilic Addition/Cyclization/Oxidation Reactions: Divergent Selective Synthesis of Brominated 2H-Chromenes, 2H-Chromen-2-ols and 2H-Chromen-2-ones

The room temperature metal-free cascade electrophilic addition/cyclization/oxidation reactions of (3-phenoxyprop-1-yn-1-yl)benzenes to divergently synthesize various brominated benzopyran derivatives (3-bromo-2H-chromenes, 3-bromo-2H-chromen-2-ols and 3-bromo coumarins) by tuning the amount of Br2 and H2O have been developed. The method exhibited high selectivity, mild reaction conditions, broad substrate scope, high efficiency, and the applicability for derivatization of the brominated products. The importance of the strategies provides a great advantage for selective synthesis of brominated benzopyran derivatives.

Base-promoted cyclization of ortho-hydroxyacetophenones with in situ generated cyclopropenes: diastereoselective access to spirobenzo[b]oxepines and related precursors

An unprecedented [5 + 2] spirocyclization route to obtain a vital class of functionalized spirobenzo[b]oxepine-cyclopropanes in good to high yields with excellent diastereoselectivities is reported. This domino reaction proceeds through a regioselective oxa-Michael addition of ortho-hydroxyacetophenones as 1,5-binucleophiles to in situ produced highly reactive cyclopropenes from 2-aroyl-1-chlorocyclopropanecarboxylates triggered by Cs₂CO₃ and the subsequent intramolecular aldol reaction under heating conditions, enabling the formation of new C-O and C-C bonds for benzo[b]oxepine ring synthesis. Moreover, at ambient temperature, the above C-O/C-C bond-forming event takes place preferentially via a [4 + 2] annulation path over a spirocyclization route, leading to substituted fused-cyclopropanes with good diastereoselectivities. Gratifyingly, further alterations of the obtained spirobenzo[b]oxepines and tetrahydrocyclopropa[b]chromenes afford fascinating classes of 4H-chromen-4-ones and cyclopenta[c]chromenes, respectively, under metal-free conditions.

BF3·OEt2-catalyzed synthesis of 2,2′-spirobi-2H-1-benzopyrans from 2H-chromenes

A new approach was developed for the construction of 2,2′-spirobi-2H-1-benzopyrancarboxylates by reacting ethyl 2-(chloromethyl)-2-hydroxy-2H-chromene-3-carboxylates with salicylaldehydes through the formation of C–C and C–O bonds in one pot.

Stereospecific Synthesis of 3,4-Dihydro-2H-naphtho-1,4-oxazin-2-ones by Unification of Benzoxepine-4-carboxylates with Chiral Amino Acid Ethyl Esters

A novel and efficient stereocontrolled method has been developed for the preparation of chiral 3,4-dihydro-2H-naphtho[1,2-b][1,4]oxazin-2-ones by the reaction of benzoxepine-4-carboxylates with chiral amino acid ethyl esters for the first time. The chiral 3,4-dihydro-2H-naphtho-1,4-oxazinones have been achieved in one step by the formation of C-N, C-C, and C-O bonds.

A facile construction of oxygen heterocycles by the reaction of benzoxepine-4-carboxylates with dihaloalkanes and activated alkynes

This manuscript describes the preparation of heterocyclic compounds such as naphtho[1,3]-dioxoles (3a-h), [1,4]-dioxines (4a-h), [1,4]-dioxepines (5a-c), [1,4]-dioxocines (6a-c) and diethyl 2-(2-ethoxy-2-oxoethyl)naphtho[1,3]dioxoles (8a-f). These heterocyclic compounds have been achieved by the reaction of benzoxepine-4-carboxylates (1a-h) with dihaloalkanes (2a-e) and activated alkyne (7a) for the first time. This work represents the first example for the construction of utile oxygen heterocycles by the formation of C-C and C-O bonds in a one step process.

La(OTf)3 catalyzed reaction of salicylaldehyde phenylhydrazones with β-ketoesters and activated alkynes: facile approach for the preparation of chromenopyrazolones

A facile approach has been developed for the preparation of chromenopyrazolones (5a–o, 7a–k) by the reaction of salicylaldehyde phenylhydrazones (3a–o) with β-ketoesters (4a, 4f–g) and activated alkynes (6a–e) in the presence of La(OTf)₃ with good yields.

Facile construction of novel heterocyclic compounds: three-component, one-pot synthesis of 2-hydroxybenzoyl-1,2-dihydropyridine-3-carboxylates, ketones, pyridone-3-carboxylates and benzopyrido-1,3-oxazole-4-carboxylates

A facile method has been developed for the preparation of novel heterocyclic compounds facilitated by 3-oxobutanoates and 1,3-diketones possessing a trihalo group. This three-component, one-pot protocol provided heterocyclic compounds without a catalyst.

A simple and efficient one-pot synthesis of 2-alkyl/aryl/pyridyl substituted 2H-chromenes

A simple and efficient protocol is demonstrated to synthesize medicinally significant new 2-pyridyl/aryl/alkyl substituted 2H-chromenes.

Carbohydrate-based first stereoselective total synthesis of bioactive cytospolide P

A facile stereoselective approach has been developed for the total synthesis of cytospolide P via Yamaguchi macrolactonization.