Acylation of the enamino tautomer of 2-azaspiro[4.5]deca-1,6,9-trien-8-ones with 5-arylfuran-2,3-diones. Crystal and molecular structure of (2Z,5Z)-3-Hydroxy-5-(6,9-dimethoxy-3,3-dimethyl-8-oxo-2-azaspiro[4.5]deca-6,9-dien-1-ylidene)-1-phenylpent-2-ene-1,4-dione