AbstractThe chemistry of several of the Diels‐Alder adducts formed by the reaction of 4,4‐diethylpyrazoline‐3,5‐dione (1) with conjugated dienes was studied with respect to reduction (hydride and catalytic) and reaction with base. Reaction of the 2,3‐dimethyl‐1,3‐butadiene adduct with lithium aluminum hydride followed by hydrogenation gave 1,3,5,6,7,8‐hexahydro‐cis‐endo‐6,7‐dimethyl‐2,2‐diethylpyrazolo[1,2‐a]pyridazine (11). Attempted conversion of this compound to 3,3‐diethyl‐cis‐7,8‐dimethyl‐1,5‐diazacyclononane (12) gave instead a compound which has been tentatively identified asN‐(2,3‐dimethyl‐4‐aminobutyl)‐2‐ethyl‐2‐methylbutanaldimine (14). Lithium aluminum hydride reduction of 4,4‐diethylpyrazolidine‐3,5‐dione (22) or the adducts formed from1and cyclopentadiene or 1,3‐cyclohexadiene gave good yields of 4,4‐diethylpyrazolidine (21). This later reduction gave a new and efficient synthetic route to the pyrazolidine ring system. Lithium aluminum hydride reduction of 5,6,7,8‐tetrahydro‐5,8‐ethano‐2,2‐diethylpyrazolo[1,2‐a]pyridazine‐1,3(2H)dione (26) followed by hydrogenolysis led to a high yield of 4,4‐diethyl‐2,6‐diazabicyclo[5.2.2]undecane (28) which is the first reported example of this ring system. Reaction of several of the adduc