Metal-free C(sp³)–H functionalization of sulfonamidesviastrain-release rearrangement

Abstract

The mild base-promoted C−H bonds functionalization of amides to obtain α,β-unsaturated imines in good yields with high chemoselectivities was achieved. Control experiments show this process involves [2 + 2] cyclization/ring-cleavage reorganization.

Cu(II)-Catalyzed N-Directed Distal C(sp3)–H Heteroarylation of Aliphatic N-Fluorosulfonamides

“…As important classes of N-centered radicals, amidyls were readily derived via the homolysis of N–X (X = F, Cl, Br, I), N–H, N–N, N–O, N–S, or azide bonds. , In particular, N -fluoroamides are stable amidyl precursors and were first utilized to achieve δ C–H halogenation . Following this work, N -fluoroamide-directed cyclization to form pyrrolidines and cyclic ureas was reported. , Meanwhile, distal C­(sp 3 )–H cyanation, alkylation, thiolation, alkynation, and other transformations of N -fluoroamides were also developed (Scheme b). Recently, in-situ-generated amidyls were captured by terminal alkynes to trigger HAT/(3 + 2) or (4 + 2) annulations .…”

Direct Synthesis of α-Amino Nitriles from Sulfonamides via Base-Mediated C–H Cyanation

“…Recently, our group reported a new reaction pattern for the cross-coupling of sulfonamides with arylimines through strain-release rearrangement. And an imine intermediate, which was generated through base-assisted HF elimination, was proposed according to control experiments and theoretical calculations . Inspired by this progress, we speculated that if the imines formed in situ from sulfonamides would selectively proceed addition reaction with nucleophile, it would provide a great opportunity for α-functionalization.…”

“…These observations show that the fluorine atom was an important driving force for this C–H cyanation. In view of the above results and previous works, , we propose a possible experimental mechanism (Scheme VI). An imine intermediate was generated from N -fluorotosylamide through a base-assisted HF elimination.…”

A facile synthesis of α,β-unsaturated imines via palladium-catalyzed dehydrogenation

“…Furthermore, some control experiments have been carried out. Either the acidic conditions excluding palladium catalysis or the basic conditions 83 by replacing HOAc with Et 3 N or K 2 CO 3 were unable to initiate the reaction with the primary mass balance being the unreacted starting material 1 (entries 21 and 22).…”

“…5a ). When freshly prepared aliphatic imine 62 was subjected to the standard reaction conditions, the desired dehydrogenation product 5 was obtained despite in a low yield of 6%; in contrast, the by-products 63 and 64 , dimerized from imine and hydrolyzed aldehyde, respectively 55 , 56 , 83 , dominated the reaction outcome along with some unidentified hydrolysis by-products. Carrying out the reaction under standard conditions by slowly adding imine 62 in dioxane (1.0 mL) using syringe pump, the yield of α , β -unsaturated imine 5 has increased to 13%, but the dimer by-product 63 (25% yield, 50% yield based on 62 ) still dominated the reaction outcome, suggesting a very fast dimerization process.…”