2-Isopropylthioxanthone-Catalyzed Divergent Functionalization of Bicyclo[1.1.0]butanes under Visible-Light Irradiation

Abstract

1,3-Functionalized cyclobutane structural motifs are ubiquitous in natural products and pharmaceuticals. Photoinduced alkylation of bicyclo[1.1.0]butanes (BCBs) offers a step-economical strategy for accessing 1,3-functionalized cyclobutane motifs. Herein, we disclose a general and mild photocatalytic protocol of bromoallylation and alkylation of BCBs in a metal, additive-free manner by using the same photocatalyst, 2-isopropylthioxanthone, in different catalytic roles. Furthermore, the synthetic utility of these products was illustrated in the synthesis of various valuable and complex cyclobutane derivatives.

Oxidative sulfonylarylation of strained C–C σ-bonds for the synthesis of 3-spirocyclic oxindoles initiated by insertion of sulfur dioxide

“…On the basis of the above experimental outcomes and observations from previous literature reports, 8–12 we propose a mechanistic scenario that is initiated by single electron transfer (SET) oxidation of the DHP 2a by (NH 4 ) 2 S 2 O 8 to deliver pyridine A and alkyl radical B (Scheme 4). 16 e Subsequently, the reaction of cyclohexyl radical B and Na 2 S 2 O 5 furnishes alkylsulfonyl radical C , which upon addition to the central C–C bond of BCB 1a generates intermediate D .…”

Overcoming a Radical Polarity Mismatch in Strain‐Release Pentafluorosulfanylation of [1.1.0]Bicyclobutanes: An Entryway to Sulfone‐ and Carbonyl‐Containing SF5‐Cyclobutanes

“…[32] Direct excitation of 35 can similarly be ruled out. [33] Thus, we propose one possible initiation mechanism that involves 1) initial complexation, e.g., of SF 5 Cl and the strain-release reagent, 2) formal Cl atom transfer concomitant with strained CÀ C bond homolysis, and 3) Cl atom abstraction from SF 5 Cl by the resultant carbon-centered radical (e.g., to form 46). This sequence would theoretically generate 2.0 equiv.…”

Overcoming a Radical Polarity Mismatch in Strain‐Release Pentafluorosulfanylation of [1.1.0]Bicyclobutanes: An Entryway to Sulfone‐ and Carbonyl‐Containing SF5‐Cyclobutanes

“…Note that SF 5 Cl does not absorb light in the visible region and homolytic S−Cl bond cleavage through direct photolysis seems unlikely [32] . Direct excitation of 35 can similarly be ruled out [33] . Thus, we propose one possible initiation mechanism that involves 1) initial complexation, e.g., of SF 5 Cl and the strain‐release reagent, 2) formal Cl atom transfer concomitant with strained C−C bond homolysis, and 3) Cl atom abstraction from SF 5 Cl by the resultant carbon‐centered radical (e.g., to form 46 ).…”