Radical Allylation of B ‐Alkylcatecholboranes

Abstract

Ethyl 2‐[(2,6,6‐trimethylbicyclo[3.1.1]heptyl‐3‐yl)methyl]propenoate 2‐(Ethoxycarbonyl)prop‐2‐en‐1‐yl phenyl sulfone Ethyl methacrylate Benzenesulfinic acid, sodium salt (+)‐alpha‐Pinene Catecholborane

Radicals in organic synthesis. Part 1

“…The methodology is amenable to large-scale preparation, as long as high-quality catecholborane is employed. 182 Furthermore, it is possible to introduce the borane moiety in an enantioselective fashion. 183 In an elegant three-step procedure, catalytic enantioselective hydroboration of acetal 238 was followed by conjugate radical addition to an activated alkene employing the Barton carbonate (N-methoxycarbonyloxypyridine-2-thione (PTOC-OMe)) as a radical trap and chain-transfer reagent.…”

“…181,182,184 Hydroboration of (þ)-a-pinene 241 with catecholborane occurs with the anticipated regio-and stereoselectivity to give the alkylborane 242 (Scheme 67). In situ reaction with an allyl sulfone and a radical initiator (di-tert-butyl hyponitrite) then gave the allylated product 243.…”

Boron — A Key Element in Radical Reactions

“…The desired products were obtained in satisfactory to excellent yields by using only 1.2 equiv of the allylsulfones with primary, secondary, and tertiary alkyl radicals [22,26,28]. Many different types of allylic sulfones bearing an ester group, a sulfonyl group, and a bromine atom react equally well (Scheme 10).…”

Tin-Free Radical Reactions Mediated by Organoboron Compounds

“…Radical allylation of B-alkylcatecholboranes using easily available allylsulfones has been described [109][110][111]. By using phenylsulfones, the fragmentation produces a stable phenylsulfonyl radical that reacts with B-alkylScheme 44 Vinylation with styryl methyl sulfoxide Scheme 45 Radical hydroallylation of alkenes catecholborane to sustain the chain reaction (Scheme 45).…”