Iodocarbocyclization reaction

'Halocarbocyclization reaction', which involves intramolecular attack of a carbon nucleophile on a double bond activated by an electrophilic halogenating reagent, has so far been uncommon. We report here that 'iodocarbocyclization reaction' of alkenyl or alkynylmalonate derivatives proceeded in good yields in the presence of Ti(OR)₄ and I₂ to give cyclized products in regio- and stereocontrolled manner. The diastereoselective iodocarbocyclization with 4-pentenylmalonate derivatives having a chiral center at the 2 or 3 position and allylmalonate having a chiral auxiliary in ester part have also been investigated. Furthermore, the reaction of 4-pentenylmalonates using a catalytic amount of a chiral titanium alkoxide in the presence of I₂ and 2,6-dimethoxypyridine proceeded with high enantioselectivity to give good yields of cyclopentane derivatives. The origin of enantioselectivity in this catalytic asymmetric reaction is also described.