The double mixed aldol condensation of 1,3-diphenylacetone with benzil in the presence of base gives an interesting product called 2,3,4,5- (tetracycline). Write a mechanism for this reaction and draw a structure for the product. This dark purple compound is an excellent Diels-Alder diene. Write the structure of the product formed from the Diels-Alder reaction of this material with methyl propanoate.