The reactions under mild conditions of deoxyguanosine with the mutagenic α,β-unsaturated carbonyl compounds methyl vinyl ketone and 2-cyclohexen-1-one were investigated. Major products from these reactions were isolated by reverse-phase high-performance liquid chromatography. The structures of the adducts were characterized by UV, proton NMR, and mass spectra and compared to those formed from reactions of acrolein and crotonaldehyde with deoxyguanosine. Analogous to the major acrolein adducts, the major adducts from reaction of deoxyguanosine with methyl vinyl ketone were a pair of equilibrating cyclic 1,N2-propanodeoxyguanosine diastereomers 3-(2-deoxy-β-D-erythro-pentofuranosyl)-5,6,7,8-tetrahydro-6-hydroxy-6-methylpyrimido[1,2-a]purin-10(3H)-one (6 and 7). The interconversion of these adducts was probably due to Setoffs base formation followed by rapid hydration resulting in isomerization at C-6. Two pairs of diastereomeric adducts were formed from the reaction of deoxyguanosine with 2-cyclohexen-1-one. The structures of these adducts were assigned as a pair of tetracyclic deoxyguanosine adducts, 3-(2-deoxy-β-D-erythro-pentofuranosyl)-5,6,7,8,9,10-hexahydro-6-hydroxy-6,10-methano[1,3]diazocino[1,2-a]purin-12(3H)-one (10 and 11), and a pair of open-chain N2-substituted adducts, 2'-deoxy-N-(3-oxocyclohexyl)guanosine (12 and 13). Characteristic UV patterns were noted at pH 13 for these adducts and the regiochemistry of their formation via Michael addition is discussed.