Tin-Free Radical Acylation Reactions with Methanesulfonyl Oxime Ether

Tin-free radical mediated C-C bond formation via the Xanthate transfer

“…Effect of Ratio of Reagents on Alkyl and Ethyl Sulfone Radical AdditionFrom these observations, we were led to believe that both the alkyl and ethyl sulfone radical concentration were of comparable significance in the reaction medium to effect the radical addition to form the oxime lactones (Scheme 90). The presumed liberated ethyl radical did not present a problem in this reaction as it did in previous work48 on sulfonyl oxime ethers. In addition, a separate experiment was performed by reacting only the alkenyl sulfone oxime ether with DLP in refluxing chlorobenzene for an Competition between Alkyl and Ethyl Sulfonyl Radical lactone, use of a large excess amount of the keto-xanthate would be required.…”

“…The dithiocarbonate then displaces another trimethylsilyl group to form the fluorinated 2'α-C-nucleoside pyrimidine dione 2.7 with regeneration of Ag + for catalytic cycle (top of Scheme 18). 44 xanthates via radical azidation 47 and radical formylation 48 with the corresponding sulfonyl azides or sulfonyl oxime ethers, respectively (Scheme 21). These allowed the incorporation of xanthates and its addition products as useful synthetic precursors towards scaffolds bearing these useful functionalities.…”

“…Ultimately, this was resolved by using a more reactive radical precursor such as an alkyl phenyl telluride which proved to accelerate the iodine atom transfer more efficiently than the alkyl iodides (Scheme 77). 48…”

“…was chosen in consideration of the anticipated poor differentiation of selectivity between primary alkyl radicals and the propagating methyl radical which are of similar HOMO energy levels. 48 Also, the ethyl radicals could be generated at a lower reflux temperature . Such a phenomenon has been similarly reported with tosyl bromide, which has been known to generate tosyl radical to undergo radical addition and cyclization.…”

“…Step Synthesis of Methyl Bis-sulfonyl Oxime Ethers Proposed strategy for heteroatom-tethered sulfonyl Obenzyl oxime ethers as carboxylate radical acceptors for thesynthesis of O-benzyl oxime ether carboxylate derivativesBuilding on our work previously on tin-free radical carbonylation48 and our recently reported improved synthetic route to bis-sulfonyl oxime ethers,147 we envisaged that the use of alkenyl heteroatom-tethered sulfonyl oxime ethers may function as potential carboxylate radical acceptors for the construction of lactone, thiolactone and maybe lactam derivatives. This would then demonstrate bis-sulfonyl O-benzyl oxime ethers as an ionic and radical bi-functional carboxylate synthetic equivalent (Scheme 85).…”