Radical-chain cyclizations thiol-catalyzed

Thiol-catalyzed Radical-chain Cyclization of Unsaturated Acetals and Thioacetals. When the unsaturated dioxolane 1 and a radical initiator, 2,2-di(t-butylperoxy)butane (DBPB), were heated at 125 °C in octane in the presence of tri(f-butoxy) silanethiol (TBST), the spirocyclic ketal 2 was formed cleanly and isolated in 92% yield (eq 1). When the reaction was performed in the absence of TBST, compound 2 was not detected. TBST is... 

Cyclization of either of the thiols (24) with acid provided the saturated thia-PGIi analogs (26) as a 2.7 1 mixture of the exo and endo isomers.271 Although many addition reactions of thiols to alkenes are radical reactions catalyzed by light, oxygen, or other radical initiators, conversion to (26) was not effected under photolytic conditions or with AIBN. A radical chain mechanism for selenothiolactonization has also been reported recently.275... 

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