6-Heptenyl radical cyclization stereoselectivity

Interesting intramolecular cyclization of 1-nitroalkyl radicals generated by one-electron oxidation of aci-nitro anions with CAN is reported. As shown in Eq. 5.44, stereoselective formation of 3,4-functionalized tetrahydrofurans is observed.62 l-Nitro-6-heptenyl radicals generated by one electron oxidation of aci-nitroanions with CAN afford 2,3,4-trisubstituted tetrahydropyrans.63 The requisite nitro compounds are prepared by the Michael addition of 3-buten-l-al to nitroalkenes. 

For the formation of six-membered rings, the chair-Uke transition state 28 (Figure 4.19) generally explains the stereoselectivity observed when hept-6-en-l-yl radicals undergo 6-exo-cyclization. Both the substituent(s) and alkene prefer to adopt pseudo-equatorial positions, therefore 1-, 3-, and 5-substitutedheptenyl radicals give predominantly trans-disubstituted cyclohexyl products, while 2- and 4-substituted heptenyl radicals give predominantly ds-disubstituted cyclohexyl products. 

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