Direct vicinal difunctionalization of alkynes through trifluoromethylation and aminosulfonylation via insertion of sulfur dioxide under catalyst-free conditions

Abstract

Direct vicinal difunctionalization of alkynes through a catalyst-free four-component reaction of Togni's reagent, alkynes, sulfur dioxide, and hydrazines at room temperature is developed, which generates (E)-3,3,3-trifluoroprop-1-ene-1-sulfonohydrazides in good yields.

Vicinal Difluoroalkylation and Aminosulfonylation of Alkynes under Photoinduced Conditions

“…In the transformation, perfluoroalkyl iodides acted as the halogen-bond donors, and organic bases were used as halogen-bonda cceptors. Based on the above experimental observation and previous reportsb y Yu and others, [9,11,12] we propose ap lausible mechanism for the photoinduced vicinal difluoroalkylation and aminosulfonylation of alkynes, which is shown in Scheme 2. We reason that initially,D ABCO·(SO 2 ) 2 combines with 2 to generate ah alogen-bonding (XB) adduct A.…”

“…Because trifluoromethylation through the generation of the CF 3 radical of Togni's reagent occurred efficiently under catalyst‐free conditions, we began our investigation with the reaction of 1‐ethynyl‐4‐methylbenzene ( 1 a ), ethyl 2‐bromo‐2,2‐difluoroacetate ( 2 ), DABCO⋅(SO 2 ) 2 , and morpholin‐4‐amine ( 3 a ) in MeCN at room temperature in the absence of any photocatalyst (Table , entry 1). However, no reaction occurred.…”

“…Therefore, we started to explore this proposed radicaltandem reactionfor the vicinal difluoroalkylation anda minosulfonylation of alkynest hrough insertionofs ulfur dioxide. Because trifluoromethylation through the generation of the CF 3 radical of To gni's reagento ccurred efficiently under catalyst-free conditions, [11] we began our investigation with the reaction of 1-ethynyl-4-methylbenzene (1a), ethyl 2-bromo-2,2difluoroacetate (2), DABCO·(SO 2 ) 2 ,a nd morpholin- 4-amine( 3a) in MeCN at room temperaturei nt he absenceo fa ny photocatalyst ( [7][8][9]. The results suggestedt hat DMF was the best choice, delivering the corresponding product 4a in 88 %y ield ( Table 1, entry 8).…”

Radicals and Sulfur Dioxide: A Versatile Combination for the Construction of Sulfonyl‐Containing Molecules

“…Alkynes ( 40 ) react with Togni's reagent ( 71 ), hydrazines ( 53 ) and DABCO ⋅ 2 SO 2 in the absence of any catalyst or additive to the difunctionalized alkenes ( 72 ) (Scheme ) . Later on, the Wu group could extend this transformation to the vicinal difluoroalkylation and aminosulfonylation of terminal alkynes .…”

Photoredox‐Catalyzed Functionalization of Alkenes with Thiourea Dioxide: Construction of Alkyl Sulfones or Sulfonamides

“…In the meantime, the combination of aryl/alkyl radicals and sulfur dioxide was discovered to provide a green and efficient way to generate sulfonyl radicals, avoiding the use of sulfonyl precursors . During the process, different radical precursors, including aryldiazonium tetrafluoroborates, aryl/alkyl halides, diaryliodonium salts and others could be reduced to generate aryl radicals, which would capture the sulfur dioxide released from DABCO·(SO 2 ) 2 or inorganic sulfites leading to aryl/alkyl sulfonyl radical intermediates. Therefore, diverse sulfonyl compounds could be prepared efficiently and environmentally friendly with the insertion of sulfur dioxide, particularly from the low‐cost inorganic sulfites.…”