Catalytic Ring Opening of β-Propiothiolactones by Dirhenium and Dimanganese Carbonyl Complexes

The catalytic ring opening of β-propiothiolactone, 1, and 3,3-dimethyl-β-propiothiolactone, 2, by Re2(CO)9(NCMe), Mn2(CO)9(NCMe), and Mn2(CO)10 has been investigated. Compound 1 was transformed into polymer (SCH2CH2CO)n (55% yield) and a mixture of new The major macrocyclic product 1,5,9,13-tetrathiacyclohexadecane-2,6,10,14-tetrone isolated in 22% yield. A second macrocycle identified as 1,5,9,13,17,21-hexathiacyclotetracosane-2,6,10,14,18,22-hexone (4, was isolated in only 2% yield. Compound 2 was converted into polymer (SCH2CMe2CO)n only; however, when applied to silica gel TLC plates, small quantities of macrocycles 3,3,7,711,11,15,15-octamethyl-1,5,9,13-tetrathiacyclohexadecane-2,6,10,14-tetrone, 5, and 3,3,7,711,11,15,15,19,19,23,23-dodecamethyl-1,5,9,13,17,21-hexathiacyclotetracosane-2,6,10,14,18,22-hexone, 6, were eluted. Macrocycles 3−6 have been characterized crystallographically. The structure of 3 is unusual for a sulfur macrocycle because the sulfur atoms are turned toward the inside of the ring to form a tetrahedral cavity. Compound 4 forms a large 6-sided 24-membered ring and crystallizes from CH2Cl2 as an inclusion compound containing 1 equiv of CH2Cl2 in the center of the ring. Compounds 5 and 6 are similar to 3 and 4, but both have lower symmetry due to transannular elongation. The catalytic reactions are promoted by light and inhibited by the radical scavenger TEMPO. It is concluded that these reactions involve radical intermediates formed by photolytic cleavage of the metal−metal bond of the dinuclear catalyst precursors.