Synthesis of novel naphthopyrans via a hetero Diels-Alder reaction
LE3 .A278 2021
Bachelor of Science
A new synthetic methodology was developed to obtain novel naphthopyrans decorated with functional groups amenable for further chemical manipulation. Starting for commercially available 2-naphthols, paraformaldehyde, cyclic secondary amines and diethyl ethoxymethylenemalonate, the synthesis was achieved in two steps. First, 2-naphthols, paraformaldehyde, cyclic secondary amines were converted to Mannich bases. Subsequently, the Mannich bases were reacted with diethyl ethoxymethylenemalonate in a microwave reactor to yield diethyl 3-(alkylamino)-1H-naphtho[2,1-b]pyran-2,2(3H)-dicarboxylates as products. The mechanism of this reaction involved a cascade of a) deamination of 2-naphthol Mannich bases to ortho-quinone methides, b) the reaction of liberated amine with diethyl ethoxymethylenemalonate to yield diethyl 2-(alkylaminomethylene)malonate, and finally c) the hetero Diels-Alder reaction of the ortho-quinone methides with in situ generated diethyl 2-(alkylaminomethylene)malonate to form the final naphtho[2,1-b]pyran products.
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