A New Method for C−H Functionalization of Aliphatic Compounds by an Unusual Photochemical Reaction of Diazoketones without Elimination of Nitrogen

Abstract

Benzophenone-sensitizedr eactions of 4-diazotetrahydrofuran-3(2H)-onesw ith H-donors such as tetrahydrofuran, 1,4-dioxane,c yclohexane and diethyle ther,o ccur without elimination of nitrogen and give rise to the corresponding N-substituted hydrazones or bis-hydrazonoethanes due to af ormal insertion of the terminal Natom of diazo group into a-CÀHb onds of ethers and aliphatic hydrocar-bons, with yields of up to 78 %. Long-wavelength UV irradiation (l > 310 nm) is most suitable fort his process, whereas oxygen molecules adequately quench the triplet excited state of the diazoketone and reduce the preparative yields of CÀH-insertion products. Hence this photochemicalr eaction of diazoketones can be used for CÀHf unctionalization of different aliphatic compounds.Scheme1.Photochemical insertion of the terminalNatom of a4 -diazodihydrofuran-3(2H)-onei nto an a-CÀHb ondofT HF.

Light-Induced Reactions of Diazotetrahydrofuranone without Elimination of Nitrogen: Experimental and Mechanistic Study

“…Instead, only Wolff rearrangement product 10 was isolated from reaction mixture (more than 90%). At the same time, hydrazone 9 was obtained from diazoketone 8 (in the yields of up to 69%) but under conditions of sensitized photolysis …”

“…It should be also noted that irradiation of diazoketone 1 in the oxygen atmosphere leads to an almost 3-fold decrease of the yield of hydrazone 3 (Scheme ). This observation can evidently serve as an argument in favor of the participation of the triplet excited states of diazofuranone 1 in the process since its concentration in the presence of the “quenching” triplets (O 2 ) goes down significantly …”

“…Thus, it was shown previously that the yield of oxetanecarboxylic acid 4 at short-wavelength excitation (>210 nm) increases by almost one order of magnitude in comparison to the longwave irradiation (>310 nm) (Scheme ). This experimental data indicates that the Wolff rearrangement of diazoketone 1 does not only occur through the lower level of S 1 when irradiated with 405 nm light but also through the upper singlet excited states populated by the short-wave irradiation of diazoketone 1 .…”

“…According to established opinion, irradiation of aliphatic diazo compounds with UV light usually gives rise to elimination of N 2 , which excludes nitrogen atoms of diazo group from the succeeding chemical transformations. − The universally known light-induced reactions of diazocarbonyl compounds without elimination of nitrogen are essentially limited to their isomerization to α-ketodiazirines. , At the same time, it was recently found that diazoketones of the tetrahydrofuran series, under distinct conditions of photochemical reaction, can avoid elimination of nitrogen molecule. Instead, they lead to insertion of the terminal N atom of diazo group into C–H bonds of organic compounds; , that is, they can be subjected to light-induced processes with conservation of nitrogen atoms of diazo group in the compounds formed (Scheme ).…”

“…In addition, light-induced and thermal reactions of α-ketodiazirine 2 (the cyclic isomer of diazoketone 1 ) were also studied to understand its role in the processes under examination. By analogy with our previous studies, , tetrahydrofuran was used in photochemical experiments as the main reaction partner with C–H bonds.…”