A convenient synthesis of benzannelated diazacycloalkanes by reductive cleavage of 1,2-polymethylenebenzimidazoles

Structurally diverse arene-fused ten-membered lactams accessed via hydrolytic imidazoline ring expansion

“…Our recent interest in N-(hetero)aryl 2-imidazolines for drug discovery 9 and scaffold-oriented synthesis 10 alarmed us due to the fact that polycyclic 2-imidazolines 5 have not been explored in the context of ring expansion (though such a possibility is indicated by the expansion of related polycyclic systems 11 and benzimidazoles 12 on treatment with aluminium hydride agents reported in the literature). When activated by protonation 13 or alkylation 14 to form 6, 2-imidazolines can undergo hydrolysis via tetrahedral intermediate 7.…”

Convenient Approach to 10‐ and 11‐Membered Azalactams

“…BH 3 or complex metal hydrides are usually used as reducing agents. Thus, we recently showed that reductive ring expansion of 1,2‐annulated benzimidazoles using DIBAL−H can serve as a convenient method for the synthesis of benzannulated 1,4‐diazamedium ring heterocycles [26] . In addition, this approach was also used for the synthesis of 1,4‐diazocine derivatives based on quaternary salts of pyrrolo[1,2‐a]imidazole [27] …”

Reductive cleavage of annulated 5,6-dihydro-2H-1,2,4-thiadiazine-1,1-dioxides: medium sized ring azasultams

“…Such selectivity is due to the formation of a more stable iminium salt 10A compared to 10B, in which the positive charge is located on the nitrogen atom bound to the electron-withdrawing SO 2 group. 48,54,55 The special role of this group in the ring expansion reaction should be noted here. Previously, we shown that under the same conditions the reductive cleavage of 4-oxotetrahydropyrimidines 4 structurally similar to 8 is greatly dependent on the saturated ring size.…”

“…Such selectivity is due to the formation of a more stable iminium salt 10A compared to 10B , in which the positive charge is located on the nitrogen atom bound to the electron-withdrawing SO 2 group. 48,54,55…”

“…As an example, we can cite the synthesis of macrocyclic polyamine alkaloids, the key stage of which is the reductive cleavage of annulated pyrimidones 4 (Scheme 1B). [44][45][46][47][48][49][50][51] In addition, we have recently shown that this approach is a convenient method for obtaining 10-and 11-membered azalactams 5 and bicyclic systems based on them. 52 Continuing research in this direction, in this work we present a convenient method for the synthesis of medium sized ring azasultams 11, by reductive cleavage of available 2,3-anulated 5,6-dihydro-2H-1,2,4-thiadiazine 1,1-dioxides 8 (Scheme 1C).…”