High performance of N-alkoxycarbonyl-imines in triethylborane-mediated tin-free radical addition.
Triethylborane-mediated tin-free radical alkylation of N-alkoxycarbonyl-imines, such as N-Boc-, N-Cbz-, and N-Teoc-imines, proceeded smoothly at a low temperature (-78 to -20 °C) to give the corresponding adducts in high yield. Although the formation of isocyanate was the major unfavorable reaction at room temperature, a one-pot conversion of N-Boc-imine to N-ethoxycarbonyl-adduct was possible through the corresponding isocyanate generated in situ. The higher performance of N-alkoxycarbonyl-imine than those of N-Ts- and N-PMP-imines is rationalized by a moderate electron-withdrawing character of an alkoxycarbonyl group that makes both addition of alkyl radical and trapping of the resulting aminyl radical by triethylborane efficiently fast.
Graduate School of Pharmaceutical Sciences, Kyoto University, Yoshida, Kyoto 606-8501, Japan. yamak@pharm.kyoto-u.ac.jp
Ken-ichi
K
Yamada
Takehito
T
Konishi
Mayu
M
Nakano
Shintaro
S
Fujii
Romain
R
Cadou
Yasutomo
Y
Yamamoto
Kiyoshi
K
Tomioka
D000478:Alkylation; D001880:Boranes / Q000737:chemistry*; D002384:Catalysis; D005609:Free Radicals / Q000737:chemistry; D007097:Imines / Q000737:chemistry*; D017953:Isocyanates / Q000737:chemistry; D008745:Methylation; D014001:Tin / Q000737:chemistry
D001880:Boranes; D005609:Free Radicals; D007097:Imines; D017953:Isocyanates; D014001:Tin; C079756:triethylborane