Diastereoselective Fe(III) mediated oxidative cyclisation reactions of cyclopropanone acetals

The Chemistry of Cyclopropanols

“…Most of the above-mentioned oxidants also successfully initiate homolytic ring opening in siloxycyclopropanes. 286,287,289,300,302,[304][305][306][307][308][309][310][311][312][313][314][315][316][317][318][319][320][321][322] An important application of the β-oxocarbonyl radicals, formed as intermediates by oxidation of cyclopropanols, is their reactions with different radical-trapping species. In their pioneering work on cyclopropanol oxidation, 285,323 De Boer and co-workers found that reactions of cyclopropanols with ferric chloride led to β-chloro ketones in good yields (Scheme 79).…”

“…296 A similar type of radical cyclization of bicyclic cyclopropanol silyl ethers was performed earlier by Booker-Milburn and co-workers, using FeCl 3 as the oxidant. 287,[308][309][310][311][312][313]329 Ring cleavage in cyclopropyloxy radical to form a β-oxopropyl radical, followed by covalent addition to flavin cofactors, is probably responsible for the irreversible inactivation of methanol oxidase by cyclo- propanol. 13,15,16,326,330 Structural studies performed with adducts isolated from this reaction have shown that a covalent bond is formed between the methylene carbon of cyclopropanol and N 5 of flavin.…”

“…The suggestion that the ring opening and bond rupture between carbon atom and leaving group is a concerted process is consistent with a remarkable sensitivity of the reaction rates to the nature of the C 2 substituent of the cyclopropane ring observed for thermal homolysis of cyclopropyl nitrites, , as well as with some other experimental 5 and theoretical data. , Oxidation of cyclopropanols with Fe(III), − Cr(VI), , Mn(III), − Pb(III), , V(V), , Mn(II), and Cu(II) 290 salts, as well as with non-metal-based oxidants, ,− is also likely to proceed by radical mechanisms. Most of the above-mentioned oxidants also successfully initiate homolytic ring opening in siloxycyclopropanes. ,,,,,− …”

The use of free radical initiators bearing metal–metal, metal–hydrogen and non-metal–hydrogen bonds in synthesis

“…Recent examples of metal initiators which have been used in this way include nickel macrocyclic complexes, 181 manganese() 182 and iron() salts. 183 Finally, (toxic) metals could be avoided completely if non-metal hydrides, bearing a weak non-metal-hydrogen bond (or bonds), could replace n Bu 3 SnH in radical chain reactions. Suitable non-metal-hydrogen bonds include carbon-hydrogen, sulfur-hydrogen, phosphorushydrogen or boron-hydrogen and some reagents of current interest are highlighted below.…”

Novel methods for the synthesis of three-, four-, five-, six- and seven-membered, saturated and partially unsaturated carbocycles

“…Iron(III) nitrate reduction of the acetals of cyclopropanones 239 generates carbon-centred free radicals that cyclise to give cyclopentanes 240 with modest to excellent diastereoselectivity (Scheme 101). 127 Acylgermane benzyloxime ethers and dimethylhydrazones are excellent radical acceptors and undergo 5-exo cyclisations about three times faster than for the parent acylgermanes. 128 Thus, irradiation of acylgermane oxime 241 in the presence of an initiator gives oximes 242 in good yield (Scheme 102).…”