Boron-tethered radical cyclizations

The radical addition to 1-alkenyl or 1-alkynylboronic esters or amides took place extremely smoothly because the boron atom stabilizes the resulting ct-radical intermediates. Bu3SnH and PhSH predominated the trans-addition products 287 in the addition to 1-alkynylboronic amides at 90 °G, whereas Bu3SnH and Ph2Ph produced the m-addition products 288 at 0°C (>98% Equation (82)).455 Intramolecular addition to 1-alkenylboronic esters has been demonstrated in boron-tethered radical cyclization that provided 1,3- or 1,4-alkanediols 290 via oxidative workup (Equation (83)).456 Inter- and intramolecular additions of alkyl radical457 and sulfonyl radical458 have also been studied. 

In a related process, boron-tethered radical cyclizations are a useful alternative to the widely used silicon versions. In some cases, rearranged products were produced as a result of an intramolecular S i reaction of a carbon-centered radical at boron (Scheme 9.13) [31]. 

DAB= Me02C- N=N— COgMe Scheme9.13 Boron-tethered radical cyclizations. 

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