Iodocyclization reaction

Several other nucleophilic functional groups can be induced to participate in iodocyclization reactions. t-Butyl carbonate esters cyclize to diol carbonates.79... 

A new approach to 2,3-disubstituted benzo[b]furans from o-alkynylphenols via 5-endo-dig-iodocyclization reaction was reported. The iodinated compounds are starting materials for a variety of substituted benzo[f>]furans <99SL1432>. 

Furo[2,3- ]pyridines can be synthesized from alkynylpyridones and iodonium sources (Scheme 31) <20060L1113>. Iodine proved to be much more effective at promoting the iodocyclization reaction than other iodonium sources (ICl, A -iodosuccinimide (NIS)). The pyridinium triiodide salt, 104, can be converted into the corresponding pyridinone by treatment with an external source of iodide. In a variation of the reaction, a one-pot synthesis of the furopyridine derivatives 105 can be achieved, with overall yields of 79-92%, by treatment with iodine followed by sodium iodide without isolation of the triiodide salt. Another similar one-pot synthesis involves 3-iodo-2-pyridones, terminal alkynes, and organic halides in a series of two palladium cross-coupling reactions (Equation 45) <20030L2441>. This reaction could also be carried out in a two-step sequence, but the overall reaction yields were typically improved for the one-pot method. 

The [2,3- ]> [2,3- ]. and [i,Z-b] isomers of 2,3-disubstituted furopyridines can be obtained from alkynes and o-iodoacetoxypyridines by a palladium-catalyzed cross-coupling reaction followed by an electrophilic iodocyclization reaction or a palladium-catalyzed cyclization in the presence of CO, as illustrated in Scheme 32 for [2,3-3] and [3,2-3] derivatives. When the pyridine ring contains strongly electron-withdrawing substituents such as carboethoxy, the reaction proceeded smoothly with benzyloxyalkynylpyridines <20020L2409>. 

The iodocyclization reaction of diethyl /3-allenic c/.a-dilluorophosphonates (13) using I2 or IC1 as the electrophile has been reported to produce six-membered a-difluoromethylenephostones (14) in moderate to good yields with high regioselectivi-ties under mild conditions.28... 

Two separate reports of electrophilic 5-endo-dig iodocyclization reactions of o-alkynylanilines leading to 3-iodoindoles were disclosed. Treatment of Sonogashira product 114 with iodine led to 3-iodoindole 115 <04TL539>. Similarly, treatment of Sonogashira product... 

One-pot phosphine-promoted domino reaaion of Morita-Baylis-Hfllman carbonates and p,Y-unsaturated a-keto esters led to 2,3-dihydrofurans which suffer secondary amine-catalyzed rearrangement to provide 2-methyl-2f/-pyrans (Scheme 2) (14EJ01189).The synthesis of bis-fused benzo-2E/-py-ran derivatives occurs through a molecular iodine mediated 6-endo-dig iodocyclization reaction of appropriate dipropargyloxyarenes (14S1807). 

Ishihara and co-workers [72] reported an iodocyclization reaction that produced polycyclic products (Scheme 13.35). These reactions were promoted by a stoichiometric amount of a chiral phosphoramidite and utilized iV-iodosuccinimide (NIS) as the iodine source. Although isomeric products were produced in the iodocyclization reaction, they could be converted to a single isomer upon treatment with chlor-osulfonic acid in 2-nitropropane. 

NIS-promoted iodocarbocychzation reaction of various functionalized 1,5-enynes occurs via a 5-endo diastereoselective process to form iodo-functionalized cyclopentenes (Scheme 6.22). Initially, the iodonium ion activates the alkynyl functionality through jt-coordination. Upon nucleophilic attack of the alkenyl moiety in an anti fashion, an iodocyclization reaction occurs and a carbocation is formed. Further, proton abstraction by the succinimide anion affords the iodo-functionalized cyclopentenes [26]. 

In 2007, it was observed by Denmark and Collins [9] that soft Lewis bases such as phosphorous(lll) species work as a potent catalyst for such reaction. In tiie presence of 10mol% of (Me2N)3P, selenolactonization of butenoic acid derivative lb witii N-phenylselenylsuccinimide rapidly proceeded to give the lactone 7 in 92% yield (Scheme 3). Ishihara and his group [10] also demonstrated triphenylphosphine as an effective Lewis base catalyst for iodocyclization reaction of 8. 

Functionahzed benzothiophenes have been generated through an iodocyclization reaction (Scheme 5.43) [65]. This transition metal-free approach to the synthesis of these compounds proceeded under very mild conditions and generated outstanding yields of the cyclization products in a few hours at room temperature. Even substrates bearing primary alcohols were successfully cyclized. 

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