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Iodophenyl templates

We used the radical relay process, chlorinating C-9 and then generating the 9(11) double bond, in a synthesis of cortisone 91 [158]. This is a substitute for manufacturing processes in which C-9 or C-ll are hydroxylated by biological fermentation. Also, with templates that directed the chlorination to C-17 of 3a-cholestanol, such as that in 90, we were able to remove the steroid sidechain [159-162]. Using an electrochemical oxidation process, we could direct chlorination by simple chloride ion with an iodo-phenyl template [163]. A general review of the processes with iodophenyl templates has been published [164]. [Pg.23]

The selectivity of the radical relay chlorination is striking. In the case of the enone (13 Sdieme 18), and in related compounds with A-ring dienones, the m-iodobenzoate template at C-17 directs chlorination to C-9 and not to die preexisting functional groups of (13). The selective chlorination of C-9 seems to be quantitative, although in the first report the A "Lalkene (14) was isolated in only 77% yield. Later work has shown that the overall introduction of this double bond can have yields in the 90-93% range, and good yields for this reaction have also been reported from another laboratory. Template-directed radical relay chlorination on the a-face of steroids has also been successful in the a/b cu-coprostanol steroid series,and in the cholestanol series with iodophenyl templates linked by amide, ether, or sulfonate functions rather than carboxylic esters. ... [Pg.47]

We also attached three steroid substrates to an iodophenyl template in 16 (Scheme 6-7) using a tris-silyl ether link, and saw that the template could direct selective radical-relay chlorination to all three tethered substrate species in the same work we reported a similar finding when a thiophene ring was the triply tethered template [49]. Thus the sulfur atom of thiophene can perform radical relay. In these triple catalytic functionalizations, the more reactive sulfuryl chloride was the preferred reagent. [Pg.167]

Some variants on the simple template-directed chlorination were also developed. For example, a steroid carrying a tethered iodophenyl group was chlorinated by electrolysis of a solution carrying chloride ion [54]. In this case, the electrolysis furnished CI2 in solution to carry a radical relay process and electrolysis also initiated the radical process by one-electron oxidation of the iodophenyl group. As another variant, the radical relay mechanism requires that it be a chlorine atom that attaches to the iodine or pyridine or sulfur to abstract hydrogen, since a complexed bromine atom is not reactive enough, but the new bond to the substrate does not have to be a carbon-chlorine link. That bond is formed by untemplated attack of the substrate carbon radical on a reagent in solution and, with an appropriate sequence of tandem reactions, other atoms can be linked to the substrate. [Pg.170]


See other pages where Iodophenyl templates is mentioned: [Pg.47]    [Pg.177]    [Pg.47]    [Pg.177]    [Pg.244]    [Pg.21]    [Pg.165]    [Pg.166]   
See also in sourсe #XX -- [ Pg.22 ]




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