Carbonate esters iodocyclization

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

Further proof of the intermediacy of the iodohydrins 85 in the formation of the hydroxy-tetrahydrofurans 80 came from two sources. Firstly, treatment with potassium carbonate led to formation of the corresponding epoxides. Secondly, by providing a second alkene function, suitably positioned to trap the iodohydrin hydroxyl by a 6-eto-trig iodocyclization, we have been able to intercept these species and hence define a new approach to substituted pyrans. Thus, treatment of the dienyl hydroxy-ester 90 with iodine and NaHCO, resulted in the formation of pyrans 92 in the ratio of 3.2 1. Presumably, initial iodohydrin formation 91 is followed by a relatively non-stereoselective 6-exo cyclization. Further chemistry of such products has yet to be carried out, especially efforts to distinguish the two iodine atoms and to cyclize to give furopyran systems <01M1001>. 

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). 

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