Intramolecular [2 + 2] photocycloaddition, 4. Synthesis of [4.<i>n</i>]cyclophanes by [2 + 2] photocycloaddition and birch reduction. A rare fragmentation of tetramethylene radical anion

Abstract

Abstract [4. n ]Metacyclophanes 6 ( n 7= 2–6), [4. n ]paracyclophanes 7 ( n = 3–6), [4. n ](4,4′)biphenylphanes 8 ( n = 3, 4), and [2.3.2.4]‐paracyclophane 9 were obtained from appropriate 1,2‐ethano[2. n ]cyclophanes 1–5 by Birch reduction. Some strained cyclophanes, like 1a, 1b , and 2a , gave linear open‐chain compounds 10 by fragmentation of the cyclobutane radical anions. The synthetic method and the fate of the cyclobutane radical anion are discussed.