Alkenes, homoallylic iodination

Cyclofunctionalization of homoallylic alcohols with bis(sym-collidine)iodine(I) perchlorate produces oxetanes in good yield if the 4-exo mode of cyclization is favored electronically by the alkene substitution pattern (Table l).14 Geminal substitution at the carbinol carbon also favors this mode of cyclization (compare entries 2 and 3 with entry 1). Substitution at C-3 leads to reaction only by the 4-exo mode (entry 4), while substitution at C-4 leads to cyclization only via the 5-endo mode (entry 5). 

Radical iodine atom transfer [3 + 2]-cycloaddition with alkene (118) using dimethyl 2-(iodomethyl)cyclopropane-l,l-dicarboxylate (117) forms cyclopentane derivative (119), through the formation of an electron-deficient homoallyl radical, followed by the addition to alkene, and cyclization via 5-exo-trig manner as shown in eq. 4.41. 

Iodine bromide. 17, 152-153 Cyclization. It is someti induced alkene functionalizati low temperatures homoallylic <... 

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