Science of Synthesis

Mondal, M.; Bora, U., Science of Synthesis: Metal-Catalyzed Cyclization Reactions, (2016) 2, 404.

Burton and co-workers have investigated the selectivity involved in the manganese(III)-mediated synthesis of exo-alkylidene heterocycles.[‌252‌] Conditions essential for the selective synthesis of 2-alkylidenepyrrolidinones by the manganese(III) acetate oxidation of 2-(alkynamido)malonates have also been studied. Consequently, in the presence of manganese(III) acetate in ethanol, the exo cyclization of 2-(alkynamido)malonates predominates and provides the Z-isomers as the major products at room or high temperature. The radical cyclization of internal alkyne substrates ‌43‌ possessing a strong tendency to form stereoisomeric products yields a high quantity of Z-selective products ‌44‌ (‌Scheme 21‌).[‌252‌] Ethyl-substituted 4-alkylidenepyrrolidinone ‌44‌ (R1 = Et) delivers maximum Z selectivity, even at room temperature. Upon increasing the bulk of the esters ‌43‌, cyclization produces (Z)-4-alkylidenepyrrolidinones ‌44‌ more selectively (‌Scheme 21‌).[‌252‌]

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References