Photochemical Decarboxylative C(sp³)–X Coupling Facilitated by Weak Interaction of N-Heterocyclic Carbene

Abstract

While N-hydroxyphthalimide (NHPI) ester has emerged as a powerful reagent as an alkyl radical source for a variety of C–C bond formations, the corresponding C­(sp3)–N bond formation is still in its infancy. We demonstrate herein transition-metal-free decarboxylative C­(sp3)–X bond formation enabled by the photochemical activity of the NHPI ester–NaI–NHC complex, giving primary C­(sp3)–(N)­phth, secondary C­(sp3)–I, or tertiary C­(sp3)–(meta C)­phth coupling products. The primary C­(sp3)–(N)­phth coupling offers convenient access to primary amines.

NaI/PPh3-catalyzed visible-light-mediated decarboxylative radical cascade cyclization of N-arylacrylamides for the efficient synthesis of quaternary oxindoles

“…All of these outcomes indicate that a radical species should be involved in this decarboxylative cascade cyclization towards oxindoles under NaI/PPh 3 catalysis. Thus, the mechanism should run in a similar fashion to related well-documented previous reports [54,[68][69][70][71][72][73][74][75][76][77], through a light-induced, phosphine-assisted, intermolecular electron transfer from sodium iodide to the redoxactive ester.…”

“…In a broader context, phosphine organocatalysis is probably still underappreciated in organic synthesis, and could lead to important future synthetic developments [61][62][63][64][65][66][67]. The NaI/PPh 3 system has been further broadly applied to the functionalization of alkenes [68][69][70], as well as to decarboxylative C(sp 3 )-X bond formation [71], cyclization of 1,7-enynes [72,73] and other reactions [74][75][76][77]. Inspired by these advances, we developed here a visible light-mediated decarboxylative radical cascade cyclization of N-arylacrylamides under NaI/PPh 3 catalysis, for the most efficient and practical synthesis of quaternary oxindoles (Scheme 1b and 1c).…”

Decarboxylation‐Initiated Intermolecular Carbon‐Heteroatom Bond Formation

“…The Barton‐type approach thus allows photochemical decarboxylations under mild conditions. The photochemical decarboxylative iodination of NHPI esters was independently disclosed by the groups of Chen [193] and Shang [194] (Scheme 17). Chen's procedure is enabled by N ‐heterocyclic carbene (NHC) catalysis with NaI as the iodine donator whereas Shang's protocol involves the use of PPh 3 in the presence of LiI [193] .…”

“…The photochemical decarboxylative iodination of NHPI esters was independently disclosed by the groups of Chen [193] and Shang [194] (Scheme 17). Chen's procedure is enabled by N ‐heterocyclic carbene (NHC) catalysis with NaI as the iodine donator whereas Shang's protocol involves the use of PPh 3 in the presence of LiI [193] . Notably, Chen's method works well for the synthesis of secondary alkyl iodides whereas the use of primary NHPI esters leads to competing formation of C( sp 3 )−(N)phth bonds by follow‐up reactions of the intermediately formed iodoalkanes.…”

Recent Advances in Organic Synthesis Using Light‐Mediated N‐Heterocyclic Carbene Catalysis

“…After this first example, they took advantage of the reactivity of these iodinated intermediates to introduce different nucleophiles as amines, alcohols or thiols (Scheme 13b). [40] Scheme 11. NHC mediated photoenolization/Diels-Alder reaction.…”