The reaction of the 1,5-diketones 1 with acetic anhydride/acetic acid in the presence of zinc chloride yields the 4-aryl-4H-pyrans 2 as main products. The annulated lactone 3 and the cyclohexene derivatives 5 are isolated as by-products. The configuration of the cyclohexanone 4a and the cyclohexenes 5 are deduced from nmr spectroscopic methods. The structure of 5b is confirmed by X-ray crystal analysis.
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The corresponding record at NLM can be accessed at https://www.ncbi.nlm.nih.gov/pubmed/16076073