Steric effects in enyne-allene thermolyses: Switch from the Myers-Saito reaction to the C2C6-cyclization and DNA strand cleavage☆

Abstract The thermal reaction of enyne-allenes 1 with large substituents ( tert. -butyl, trimethylsilyl) at the acetylene terminus leads to C 2 C 6 cyclization products presumably via an intermediate benzofulvene biradical, whereas with a hydrogen substituent the expected Myers-Saito cycloaromatization product is formed. Effective DNA strand scission can be observed when no intramolecular pathway is available.