Synthesis of 4-(alkoxyamino)chroman-2-ones via 6-exo-trig cyclization of carbon-centered radicals into oxime ethers

摘要

4-(Alkoxyamino)chroman-2-ones were synthesized via a 6-exo-trig cyclization of alkyl radicals obtained from alpha-bromoesters containing an oxime ether group. In the case of secondary bromides, the best results were achieved using tris(trimethylsilyl)silane as the chain transfer agent and Et3B as the initiator in dichloromethane at room temperature; the corresponding chromanones were produced in 58-70% yield. Low yields of the cyclized compounds were obtained in the case of tertiary alkyl bromides (20-25%). Products of premature reduction of carbon-centered radicals and addition of ethyl radicals to C=N bond were also observed.