REACTIONS OF FORMALDEHYDE WITH METHYLENE COMPOUNDS .2. PRODUCTS FROM PENTANE-2,4-DIONE

Reaction of pentane-2,4-dione with excess of formaldehyde affords an impure 1:2 condensation product, 3,3-bis-(hydroxymethyl)pentane-2,4-dione. With less formaldehyde, the products include the 2:2 condensation product, 2-methyl-3,5,5-triacetyltetrahydropyran-2-ol (VII), the 2:3 condensation product, 1,5-diacetyl-2,6-dimethyl-3,7-dioxabicyclo[3,3,1]nonane-2,6-diol (X), and the 3:4 product, 1,7-diacetyl-2,4,8,10-tetramethyl-3,5,9,11- tetraoxatetracyclo [5,5,3,04,14,010,14]pentadecane-2,8- diol (XIV). The 2:3 product loses the elements of water to afford 1,5-diacetyl-2,6-dimethyl-3,7,10-trioxatricyclo[3,3,1,12,6]decane (XI) and with piperidine undergoes a C→O acetyl migration to give 2,2-diacetyl-4-methylene-5-oxohexyl acetate (XIII). The 3:4 product is converted under acid conditions into 2,2-diacetyl-3-(5,5-diacetyl-5,6-dihydro-2- methylpyran-6-yl)-propyl acetate (XV) which with base affords the 3,3-diacetyl-2,3-dihydro-6-methyl-5-(2-methylene-3-oxobutyl)-pyran (XVI).