Two Approaches to Diverting the Course of a Free-Radical Cyclization: Application of Cyclopropylcarbinyl Radical Fragmentations and Allenes as Radical Acceptors
2009-11-20T00:00:00Z (GMT) by
Free radical cyclization of <b>4</b> and <b>7</b> gave the expected cyclization-reduction products (<b>5</b> and <b>8</b>) along with considerable amounts of products derived from a cyclization−atom transfer−secondary cyclization process (<b>6</b> and <b>9</b>). Two approaches to avoiding these unexpected products were explored. Use of a cyclopropylcarbinyl fragmentation avoided the secondary cyclization reaction (<b>25</b> or <b>43</b> → <b>26</b> or <b>44</b>), whereas use of an allene as a radical acceptor avoided the atom-transfer reaction altogether (<b>49</b> → <b>52</b>).