Synthesis of fused chromene-1,4-naphthoquinones via ring-closing metathesis and Knoevenagel-electrocyclization under acid catalysis and microwave irradiation

Two complementary methodologies involving olefin ring-closing metathesis and Knoevenagel-electrocyclization were utilized for the synthesis of α-xyloidones and fused chromene-1,4-naphthoquinones 5f-n and 6. The latter methodology was performed under acid catalysis or microwave irradiation allowing the synthesis of α-xyloidones 5f-j in moderate to good yield, which could not be obtained via the Knoevenagel-electrocyclization method. On the other hand, the lawsone bis-alkylation (C and O) then RCM olefin enabled the preparation of simple xyloidone 5m-n and the oxepin-1,4-naphthoquinones 6.