Nickel powder promoted 5-endo radical cyclisations. A concise approach to Erythrina alkaloids

Some aspects of radical chemistry in the assembly of complex molecular architectures

“…This is illustrated by the short, six-step total synthesis of (±)-3-demethoxy-erythratidinone ( 170 ) displayed in Scheme 31 [71]. In this approach, trichloroacetenamide 167 , trivially obtained in two steps from monoprotected cyclohexanedione, is subjected to the cyclisation sequence to give diene 168 , which smoothly undergoes an intramolecular Friedel–Crafts reaction to generate the last ring in intermediate 169 .…”

Radical Cyclization of Trichloroacetamides: Synthesis of Lactams

“…This methodology was successfully applied to the total synthesis of erythrina 65 and lycorane 66 alkaloids, through the cyclizations 90 → 91 and 4 → 92, respectively, as key steps (Scheme 54).…”

From Simple Furans to Complex Nitrogen‐Bearing Aromatic Polycycles by Means of a Flexible and General Reaction Sequence Initiated by Singlet Oxygen

“…In the case of menthofuran with the dimethoxyphenyl aromatic partner, when the process was carried out according to the developed protocol (without purification of intermediates), and, when given a slightly longer reaction time with HCOOH, another oxidation was seen to take place giving the unsaturated product 8 ba (as a single isomer, Table 2, entry 4). Presumably, this occurs through hydrogen abstraction from intermediate 7 ba (and likewise 7 ac and 7 bc) to afford the highly stabilised tertiary radical (at C1, Scheme 2), which is subsequently oxidised to the corresponding cation [29] from which the double bond is generated following elimination of a proton. Support for this scenario comes in the form of diene 9, isolated as the only product of the one-pot reaction sequence involving menthofuran and a simple unactivated aromatic partner (5 b!9,Scheme 2).…”