Exploring aminoalkynols for the synthesis of iodo-dihydrofuran heterocycles by electrophilic cyclization and exploiting its unusual reactivity for the synthesis of α-iodoketones

摘要

Electrophilic cyclization in recent years has grown exponentially and has become the most sought-after method for the synthesis of heterocyclic molecules. The attention to electrophilic cyclization is due to its versatility, providing various options in terms of the catalyst/reagent, the type of C-C unsaturation bond and the nucleophile. A variety of heterocyclic molecules can be produced by careful design and tuning of starting substrate specific for the heterocycle of interest. Metals are the most commonly employed catalyst for such cyclization reactions. Halogens are also known to mediate such reactions and provides a cheaper option over metal mediated reactions. Halogens, specially bromine (Br) and iodine (I) also provide an opportunity to further functionalize the molecule by various coupling reactions. In this thesis a new methodology has been developed for the synthesis of iodo-dihydrofuran heterocycles utilizing molecular iodine (I2) mediated electrophilic cyclization chemistry. The developed methodolgy involves aminoalkynols as the starting substrate which cyclizes to dihydrofurans regioselectively giving good yields of the products. The developed methodology is quick, comparitively simpler and offers a easier product isolation. The method developed also provides an oppurtunity to further functionalize the molecule utilizing the iodine atom present in the product molecule. Various C-C and C-N copuling reaction were succesfully employed to functionalize the product molecules and diversify the dihydrofurans. An unusual reactivity of aminoalkynols was discovered during the course of the first study, the chemistry of the reaction was identified and the product was analysed to be an α-iodoketone. The observed chemsitry is rare in terms of iodonium activation of alkynes for the conversion to α-iodoketones and the report is first of its kind in terms of iodine monochloride (ICl) as the electrophilic source. This unusuall reactivity was well exploited and succesfully applied for the synthesis of various substituted α-iodoketones from aminoalkynols.