Zum Mechanismus der sequentiellen Radikal‐Cyclisierung von (Bromomethyl)silyl‐ethern terpenoider Alkohole

On the Mechanism of Sequential Radical Cyclization of (Bromomethyl)silyl Ethers of Terpernoid Alcohols The cyclic products of the Bu 3 SnH‐promoted radical reaction of ( E )‐1‐[(bromomethyl)dimethylsilyloxy]‐2‐methylhept‐2‐ene ( 6 ) consists to 98% of a 1:2 mixture of (±)‐(4 RS ,5 RS )‐ and (±)‐(4‐ RS ,5 SR )‐4‐butyl‐2,2,5‐trimethyl‐1‐oxa‐2‐silacyclohexane ( 8a and 8b , respectively). It is, therefore, concluded that the 6‐‘ endo ’→5‐‘ exo ’ tandem cyclization of the 5‐mehtyl‐3‐oxa‐2‐siladeca‐5,9‐dien‐l‐yl radical (reaction 1 → 2 ) is not necessarily a concerted process, but may be explained as a sequence of individual steps via free‐radical intermediates.