Enamines from the biomass derivative Cyrene and reactions with isocyanates and ketenes
To extend the chemical space accessible from the biomass-derived platform chemical Cyrene, enamines have been prepared and their reactions with selected electrophiles have been examined. The crystalline enamines prepared from morpholine (89% yield) and piperidine (79% yield) were stable and showed excellent reactivity with isocyanates, isothiocyanates and ketenes to give amides, thioamides or cyclobutanones, respectively.
Skeletal rearrangement of 6,8-dioxabicyclo[3.2.1]octan-4-ols promoted by thionyl chloride or Appel conditions
A skeletal rearrangement of a series of 6,8-dioxabicyclo[3.2.1]octan-4-ols has been developed using SOCl2 in the presence of pyridine. An oxygen migration from C5 to C4 was observed when the C4 alcohols were treated with SOCl2/pyridine, giving a 2-chloro3,8-dioxabicyclo[3.2.1]octane ring-system via the chlorosulfite intermediate. Analogous allylic alcohols with endocyclic and exocyclic unsaturations underwent chlorination without rearrangement due to formation of allylic cations. The rearrangement was also demonstrated using Appel conditions, which gave similar results via the alkoxytriphenylphosphonium intermediate. Several reactions of the products were investigated to show the utility of the rearrangement.
Intermolecular Enamine Mizoroki–Heck Reactions on a Bio-Derived Scaffold
The intramolecular enamine-Mizoroki–Heck reaction allows for the construction of nitrogen-containing heterocycles, although the related intermolecular version is less known. The reactions of enamines derived from Cyrene were investigated under Mizoroki–Heck conditions. An optimization study was used to identify that 1.5 mol % Pd(dba)2 with PCy3 in xylene at reflux temperature gave the highest yield with electron-rich aryl iodides. Arylation occurred predominantly at the C–N center of the enamine, while the diastereoselectivity was dependent on the nitrogen substitution in the enamine.