Bioactive Phytochemicals: Efficient Synthesis of Optically Active Substituted Flav-3-enes and Flav-3-en-3-o-R Derivatives

Scheme 6

Synthesis of 4-substituted flav-3-en-3-o-R substituent. Reagents and conditions: (i) Phlorog., AgBF₄, THF, reflux, 61% (19a), 59% (19b); (ii) 19a, Py, (CH₃CO)₂O, 40°C, 92%; (iii) 19b, Pd(OH)₂, H₂, EtOAc/MeOH, rt, 95%; (iv) Py, (CH₃CO)₂O, 40°C, 90%; (v) 19b, THF, Na/EtOH, NaBH₄, rt, 99%; (vi) Pd(OH)₂/C, H₂, EtOAc/MeOH, rt, 94%.