A Facile Synthesis of Anhydro-dimers of o-Hydroxybenzaldehydes

Sulphated Zirconia as an Eco-Friendly Catalyst in Acylal Preparation under Solvent-Free Conditions, Acylal Deprotection Assisted by Microwaves, and the Synthesis of Anhydro-Dimers of o-Hydroxybenzaldehydes

“…The classic method of dimerization employs acetic anhydride as the dehydrating agent and solvent using a catalytic amount of sulfuric acid [ 42 ], this method provides a 65% of the dimer 3. Clearly, the advantages with our experimental conditions are the reusability of the catalyst, the easy separation of pure products and carrying out the reaction in conditions of green chemistry.…”

Access to Pyrrolocoumarins through DBU‐Mediated Coupling of 2‐Oxo‐2H‐chromene‐3‐carbaldehydes and Phenacyl Azides

“…However, its formation can be expected in lines with the reported formation of anhydro dimer of 2-hydroxybenzaldehydes. [11] The mechanistic rationalization for the formation of pyrrolocoumarin 3 from the DBU mediated coupling of 4-chloro-2-oxo-2H-chromene-3-carbaldehydes 4 and phenacyl azide 2 is depicted in Scheme 4. Benzylmercaptan couples with 4-chloro-2-oxo-2H-chromene-3-carbaldehydes 4 in the presence of DBU to yield 4-(benzylthio)-2-oxo-2H-chromene-3-carbaldehydes 1.…”

“…DBU is considered as a non-nucleophilic base and it has been reported to couple phenacyl azides with aldehydes to yield 2-azido-3-hydroxypropan-1-ones. [11] We, therefore, tried to couple 4-(benzylthio)-2-oxo-2H-chromene-3-carbaldehyde (1 a) with phenacyl azide (2 a) using DBU as a base. To our surprise, instead of the expected 2-azido-3-hydroxy-propan-1-one the reaction led to the formation of pyrrolocoumarin 3 a exclusively (Scheme 1).…”

Synthesis of 6,12-Disubstituted Methanodibenzo[b,f][1,5]dioxocins: Pyrrolidine Catalyzed Self-Condensation of 2′-Hydroxyacetophenones

“…Aware of the limitations of the available methods for the preparation of methanodibenzo[ b , f ][1,5]dioxocin, and intrigued by the singular reactivity of pyrrolidine in promoting the self-condensation reaction, we set out to investigate and optimize the reaction conditions to efficiently construct such a polycyclic core from the self-condensation of three 2′-hydroxyacetophenone molecules. Importantly, previously reported attempts to dimerize β-hydroxy ketones using acidic/dehydrating conditions proved unsuccessful, although 6H,12H-6,12-epoxydibenzo[ b , f ][1,5]dioxocins could be obtained from the dimerization of salicylaldehydes [43,44].…”