Radical cyclopentyloxyl

A highly strained cyclopentyloxyl radical formed from compound (272) in situ induces (3-cleavage as shown in eq. 3.110. 

Rate constants for some alkoxyl radical fragmentations are shown in Fig. 9. The tcrt-butoxyl radical (26) fragmentation to acetone and the methyl radical has been studied for years, but the rate constant shown below is from a very recent work that employed time-resolved ESR methods [2]. The cumyloxyl radical (27) fragmentation was studied directly by LFP methods, taking advantage of the IR and UV absorbances of this radical [57]. The rate constants for the reversible ring opening of the cyclopentyloxyl radical (28) were determined by competition kinetics [58], and one should note that the kinetic values are at 80 °C. 

Further, substituted cyclopentyloxyl radical 2 is probably a key intermediate in the biosynthesis of the human hormone prostacycline (PGI2) (3) from endoperoxide PGH2 (1) and the enzyme PGI-synthase. Intermediate 2 is trapped intramolecularly by addition to the olefinic double bond in the proximate side chain to afford, in subsequent transformations, eicosanoid 3 (Scheme 1) [7]. 

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