Thermal Cycloaddition Reactions of Thiocarbonyl Compounds. 4. Synthesis of Novel Adamantane-2-spirothiaheterocycles via Cycloaddition Reactions of Adamantanethione with Conjugated Dienes

Article abstract of DOI:10.1021/jo00353a008

Thermal cycloaddition reactions of adamantanethione (1) with conjugated dienes such as cyclopentadiene, 2,3-dimethyl-1,3-butadiene, piperylene, isoindole, and isobenzofuran occured smoothly at 20-110 deg C to afford <4 + 2> cycloadducts (3a, 3b, 3d, 23a, and 23b) in good yields.On the other hand, similar treatment of 1 with isoprene gave a 45:55 mixture of regioisomers 3e and 4e.Furthermore, reaction of 1 with Danishefsky's diene (2f) occurred at 110 deg C to afford regioselectively adamantane-2-spiro-(2'-thiacyclohex-5'-en)-4'-one (9) in a good yield after desilylative elimination of the initial adduct.On the other hand, reaction of thiobenzophenone (11) with 2f gave 2,2-diphenyl-6-methoxythiacyclohexan-4-one (14) and 2,2-diphenylthiacyclohex-3-en-5-one (17) in 16percent and 52percent yields, respectively.The nature of these cycloadditions is discussed on the basis of FMO and steric effects.