Iodocyclization. stereocontrol

Examples of highly stereoselective iodocyclizations of 5-aminocyclohexenes to generate azaspiro-cycles are shown in equations (99)225 and (100).225b The stereocontrol in these examples is attributed to the effect of the f-butyldimethylsilyloxy substituent.225... 

In order to explain the high stereocontrol occurring in the iodocyclization of 3-acylamino-2-methylenealkanoates, the conformational space of the starting molecule and the potential energy surface (PES) for the cyclization reaction was explored at the DFT level the polarized continuum formalism (PCM) for chloroform was used in order to consider the solvent effect. The observed stereoselection [(9) (10)] was (de)... 

For the stereocontrolled formation of nonterminal vinyl iodides the iodocyclization of allenes proved to be very useful. When the trichloroacetimidate 638 was treated with iodine in the presence of base, the (Z)-vinyl isomer 639 was generated as the major product in a kinetically controlled electrophilic addition-cyclization sequence [242],... 

Numerous substrate variations can be explored as a com-plemoit to the ether transfer. Therefore, 1,1-disubstitution in the homoallylic alcohol starting material was envisioned as an avenue to access tertiary ethers. The synthesis of such fimctionahty from stereoselective C—O bond formation is rare. To access the issue of the stereoselective synthesis of calcitriol lactone, a major metabolite of vitamin D3 developed by Hoffmann-La Roche U.C. Riverside, Jonhson and Chan synthesized tertiary ethers in high stereocontrol through iodocyclization of the coiresponding tert-butyl carbonate 161 using Barlett s procedure (Scheme 37.32). ... 

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