Radicals exocyclic five-membered ring

The relative amount of peroxide product and epoxy-alcohol is intimately dependent on the structure of the intermediate radical. In Table I is presented the product distribution of peroxide and Sfli product (epoxy-alcohol) for a series of cyclic peroxide alkyl-radicals. Note that the exocyclic five-membered ring radicals and lead predominately to peroxide as does the endocyclic seven-membered ring radical The exocyclic six-membered ring... 

It has been shown" that isomerization of the exocyclic allylic system of the five-membered ring D of kaurenols depends on the orientation of the C(15) hydroxyl group. The total synthesis of methyl atis-16-en-19-oate, a tetracyclic diterpenoid possessing a bicyclo[2.2.2]octane skeleton, has been accomplished" using a homoallyl-homoallyl radical rearrangement process of methyl 12-hydroxykaur-16-en-19-oate monothioimid-azolide (280) as the pivotal step. Two plausible mechanisms have been presented" ... 

Cyclization of vinyl radicals. Vinyl radicals formed by reduction of vinyl halides with tri-n-butyltin hydride (AIBN, hv) can undergo intramolecular cyclization to a suitably situated double bond. When either a five- or a six-membered ring can be formed, the former ring is favoured. When cyclization could lead to a six- or seven-membered ring, only the former is formed, as in the cyclization of 1 to 2. The cyclization of 3 to 4 is particularly interesting because the exocyclic double bond is formed at a predictable and useful position, and because a quaternary centetis formed without difficulty. 

The mass spectra of a number of heterocyclic compounds have been reported. The fragmentation patterns of thiophosphoryl derivatives of phosphorinanes are sensitive to stereochemistry, thus for the series (95) facile loss of the HS radical is indicative of an axial PS bond. The seven-membered heterocycles (96 Ch = S, Se) undergo a remarkable migration of sulphur or selenium from phosphorus to carbon with ring cleavage. While exocyclic P-C bonds of five-and six-membered heterocycles in the phosphonic class may be readily cleaved with retention of the phosphorus ring system, the seven-membered ring (97) exhibits facile expulsion of a phosphorus radical. ... 

---