Dissecting Alkynes: Full Cleavage of Polarized C≡C Moiety via Sequential Bis-Michael Addition/Retro-Mannich Cascade

Abstract

The reaction of diaryl ketoalkynes with 1,2-diamino ethane leads to the full scission of the triple bond with the formation of acetophenone and imidazoline fragments. In this transformation, one of the alkyne carbons undergoes formal reduction with the formation of three C-H bonds, whereas the other carbon undergoes formal oxidation via the formation of three C-N bonds (one π and two σ). Computational analysis confirmed that the key fragmentation step proceeds via a six-membered TS in a concerted manner. Both amines are involved in the fragmentation: the N-H moiety of one amine transfers a proton to the developing negative charge at the enolate oxygen, while the other amine provides direct stereoelectronic assistance to the C-C bond cleavage via a hyperconjugative n(N) → σ*(C-C) interaction.

Peculiarities of the cascade cleavage of the polarized C≡C-fragment in α-ketoacetylenes on reaction with ethylene diamine

“…These results are in agreement with our previous finding, 7 which support that an increase in temperature during the reaction between ketoacetylenes and EDA even by 25 °C (from 100 °C to 125 °C) leads to significantly larger yields of monoadduct А1 inter fragmentation products (by 20-40%).…”

“…This area of organic chemistry has attracted considerable research attention. 5 Earlier we reported 6,7 that the reaction of diarylketoacetylenes with EDA affords acetophenones and 2-substituted imidazoline derivatives. This fragmentation involves total cleavage of the triple bond via three formal reductive stages to form three C-H bonds, whereas other carbon undergoes formal oxidation, i.e.…”

Experimental and Theoretical Study of an Intramolecular CF3‐Group Shift in the Reactions of α‐Bromoenones with 1,2‐Diamines

“…A few years ago we described a similar fragmentation of trifluoromethylated haloalkenes and alkynes to derivatives of carboxylic acids 14. An analogous fragmentation has recently been demonstrated for acetylenic ketones by Vasilevsky and Alabugin and co‐workers 15. In both cases the key step proceeds via a six‐membered transition state and leads to benzoic acid derivatives as the principal fragmentation products.…”

Scandium triflate catalyzed unexpected cleavage of C-C bonds in ynones

“…Extensive literature study reveals that there exist quite a few reports catalytic cleavage of C(sp)-C(sp) bonds of unactivated alkynes. [19][20][21][22][23][24] However, such kind of C(sp)-C(sp) bond cleavage in ynones are remains uncommon 25 . Similarly, it should be noted that the such kind of cleavage in 1,3-diketone 26,27 has literature precedence; however, the use of naked H + , [28][29][30][31][32] amines 33 or strong bases [34][35] are necessary and the reactions are low yielding.…”