Cyclization quadruple

When a true free radical, such as 3b or 5a, is formed, it reacts further following the normal pattern of radical reactions [11]. For instance, radical 3b cyclizes from the conformation shown to give radical 5b stereo- and regiospecifically. In appropriately designed systems it is possible to perform tandem, triple, and even quadruple cyclizations [12-14],... 

A wide variety of tandem, triple [12], and even quadruple [13, 14] cyclizations can be performed with multiply unsaturated 1,3-dicarbonyl compounds as shown in Eq. (1) [14] this provide intermediates for steroid and terpene syntheses. High levels of asymmetric induction can be achieved with phenylmenthyl acetoacetate... 

Manganese(III)-mediated radical reactions have become a valuable method for the formation of carbon-carbon bonds over the past thirty years since the oxidative addition of acetic acid (1) to alkenes to give y-butyrolactones 6 (Scheme 1) was first reported by Heiba and Dessau [1] and Bush and Finkbeiner [2] in 1968. This method differs from most radical reactions in that it is carried out under oxidative, rather than reductive, conditions leading to more highly functionalized products from simple precursors. Mn(III)-based oxidative free-radical cyclizations have been extensively developed since they were first reported in 1984-1985 [3-5] and extended to tandem, triple and quadruple cyclizations. Since these additions and cyclizations have been exhaustively reviewed recently [6-11], this chapter will present an overview with an emphasis on the recent literature. 

Triple and quadruple cyclizations. A wide variety of triple and even quadruple [49, 50] cyclizations can be carried out with multiply unsaturated 1,3-dicarbonyl compounds. Oxidative triple cyclization of 82 affords 70% of 83 since the cyclo-pentanemethyl radical is oxidized to a double bond by Cu(II) (Scheme 26) [47]. Similar cyclization of 84 provides 43% of 85 (Scheme 27) [49]. Oxidative cyclization... 

---