The radical azidoalkylation of alkenes that was initially developed with α-iodoesters and α-iodoketones was extended to other activated iodomethyl derivatives. By using iodomethyl aryl sulfones, the preparation of γ-azidosulfones was easily achieved. Facile conversion of these azidosulfones to homoallylic azides using a Julia–Kocienski olefination reaction is reported, making the whole process equivalent to the azidoalkenylation of terminal alkenes.
Two-Step Azidoalkenylation of Terminal Alkenes Using Iodomethyl Sulfones
Sci. China Chem. 2019, 62, 1504–1506
A concise route for the preparation of two simple optically pure indolizidin-5-ones has been developed. The key chain elongation process was achieved using a triethylborane/catechol mediated hydroalkylation of Boc-protected 2-vinylpyrrolidines. By using complementary strategies, these two bicyclic lactams can be alkylated with complete control of the stereochemistry at C(5) and their conversion to a variety of indolizidine alkaloids such as coniceine, indolizidine 209D and 167B, 5-epi-indolizidine 249A and monomorine has been reported in the literature.
Radical-mediated hydroalkylation of 2-vinylpyrrolidine derivatives: a versatile entry into indolizidine alkaloids
Eur. J. 2019, 25, 11646–11649.
A very concise total synthesis of (+)-brefeldin C starting from 2-furanylcyclopentene is described. This approach is based on an unprecedented enantioselective radical hydroalkynylation process to introduce the two cyclopentane stereocenters in a single step. The use of a furan substituent allows a high trans diastereoselectivity to be achieved during the radical process and it contains the four carbon atoms C1–C4 of the natural product in an oxidation state closely related to the one of the target molecule. The eight-step synthesis requires six product purifications and it provides (+)-brefeldin C in 18 % overall yield.
L. Gnägi, S. V. Martz, D. Meyer, R. M. Schärer, P. Renaud
A Short Synthesis of (+)-Brefeldin C through Enantioselective Radical Hydroalkynylation
Angew. Chem. Int. Ed. 2019, 58, 14240–14244.
An operationally simple method to affect an atom-transfer radical addition of commercially available ICH2Bpin to terminal alkenes has been developed. The intermediate iodide can be transformed in a one-pot process into the corresponding cyclopropane upon treatment with a fluoride source. This method is highly selective for the cyclopropanation of unactivated terminal alkenes over non-terminal alkenes and electron-deficient alkenes. Due to the mildness of the procedure, a wide range of functional groups such as esters, amides, alcohols, ketones, and vinylic cyclopropanes are well tolerated.
D. C. Tappin, W. Michalska, S. Rohrbach, P. Renaud