Carbohydrate‐Based Studies Toward the Synthesis of Hamigeromycin E: A Stereoselective Total Synthesis of an Isomer of Zeaenol

A stereoselective synthesis of 14‐membered macrolide hamigeromycin E ( 6 ) has been studied by employing ortho‐lithiated formylation, Barbier allylation, Julia–Kocienski olefination, Mitsunobu esterification, and ring‐closing metathesis (RCM) reactions. The final RCM reaction did not provide the target molecule. This study has prompted us to synthesize a stereoisomer of zeaenol and accomplish the total synthesis with the above protocols.     

A facile approach for the synthesis of novel substituted 4H-chromenes and condensation reactions of 4H-chromenes leading to chromenopyrrolones and triazolylchromenopyrrolones

A facile method has been developed for the synthesis of 4H-chromene-3-carboxylates 3a–d by the nucleophilic substitution reaction of 2-hydroxy-2H-chromene-3-carboxylates 2a–d with triethylsilane in the presence of BF₃·O(C₂H₅)₂. Cyclocondensation of 4H-chromene-3-carboxylates 3a–d with benzylamines 4a–d afforded a series of 2,3-dihydrochromenopyrrolones 5a–p and with propargylamine afforded 2-propynyl-2,3-dihydrochromenopyrrolones 6a–d. Click reaction of 6a–d with benzyl azides 7a–d provided a series of 1H-1,2,3-triazolylmethyl-2,3-dihydrochromenopyrrolones 8a–p. Thus synthesized compounds 3a–d, 5a–p, 6a–d, and 8a–p are novel heterocyclic compounds and being reported for the first time.     

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

Wittig homologation of 2-(chloromethyl)-2H-chromen-2-ol derivatives 2a–t with (ethoxycarbonylmethylene)triphenylphosphorane provided the 2-oxoethylidene-2,3-dihydrobenzoxepine-4-carboxy-lates 3a–t with Z (cis) selectivity. Various basic catalysts were studied for the reaction of 2-(chloromethyl)-2H-chromen-2-ol 2a with the combination of Wittig reagent to provide compound 3b. The reaction of 2-(chloromethyl)-2H-chromen-2-ol 2a with other Wittig reagents, such as methylene(triphenylene)phosphorane and (1-ethoxycarbonylethylidene)triphenylphosphorane provided ketone derivative 4a rather 2-oxoethylidene derivative 3b. The ketone derivative 4a was reacted with Wittig reagent (ethoxycarbonylmethylene)triphenylphosphorane to give 2,3-dihydrobenzoxepine-4-carboxylate 3b. The present approach is novel, straight forward and being reported for the first time.     

Facile Synthesis of Substituted Ethyl 2‐(Chloromethyl)‐2‐hydroxy‐2H‐1‐benzopyran‐3‐carboxylates

Ethyl 2‐(chloromethyl)‐2‐hydroxy‐2H‐chromene‐3‐carboxylates 2a – 2j have been synthesized by reaction of substituted salicylaldehydes with ethyl 4‐chloro‐3‐oxobutanoate, in the presence of piperidine in CH₂Cl₂ at room temperature, in good yields.