An Unexpected Rearrangement That Disassembles Alkyne Moiety Through Formal Nitrogen Atom Insertion between Two Acetylenic Carbons and Related Cascade Transformations: New Approach toSampangineDerivatives and Polycyclic Aromatic Amides

Abstract

This work analyzes multiple new reaction pathways which originate from intramolecular reactions of activated alkynes with the appropriately positioned multifunctional hemiaminal moiety. Combination of experimental substituent effects with Natural Bond Orbital (NBO) analysis revealed that alkyne polarization controls partitioning between these cascades. A particularly remarkable transformation leads to the formation of six new bonds at the two alkyne carbons due to complete disassembly of the alkyne moiety and formal insertion of a nitrogen atom between the two acetylenic carbons of the reactant. This reaction offers a new synthetic approach for the preparation of polycyclic aromatic amides with a number of possible applications in molecular electronics. Another of the newly discovered cascades opens access to substituted analogues of Sampangine alkaloids which are known for their antifungal and antimycobacterial activity against AIDS-related opportunistic infection pathogens.

Reaction of guanidine with peri-substituted (R-ethynyl)-9,10-anthraquinones bearing electron-donating substituents

“…It should be noted that for the substrates containing elec tron withdrawing substituents, if the corresponding amino ketones 2 were formed, then only as minor products. 1 The data obtained agree with the results reported earlier, 1 according to which the reaction of guanidine with 1 [(4 methoxyphenyl)ethynyl] 9,10 anthraquinone mainly gives amino ketone of the type 2.…”

“…These transformations are of interest from the point of view of exo/endo selective ring forma tions (the Baldwin's rules). 3 For instance, it was shown 1,2 that the reaction of peri (R ethynyl) 9,10 anthraquinones with guanidine leads to 1 aryl 7H dibenzo [ [1,3]diazocine 2,9 dione (IV), 12 (9,10 dioxo anthracen 1 yl) 2,2 dimethyl 2H phenanthro[2,1,10 def] chromen 1,6 dione (V), and 12 amino 2,2 dimethyl 2H chromeno [4,5,6 cde]benzo[h]quinoline 1,6 dione (VI) systems (Scheme 1), with the ratio and type of the reaction products being dependent on the structure of acetylene substituent.…”

Regioselective One‐Pot Synthesis of Triptycenes via Triple‐Cycloadditions of Arynes to Ynolates

“…Thec alculated reaction barrier is remarkably low. [23] This is aconceptually unique application of alkynes in synthesis and the first example of the formal insertion of three arynes into at riple bond. s * CÀO hyperconjugative assistance.…”

Radical 1,2‐O→C Transposition for Conversion of Phenols into Benzoates by O‐Neophyl Rearrangement/Fragmentation Cascade

“…Third, the radical should be sufficiently reactive to initiate the key 1,2 O!C transposition through an ipso attack at the aromatic ring, followed by C À O bond cleavage (O-neophyl rearrangement). [4,5] For this purpose, substituents X and Z should not deactivate the radical center through excessive stabilization and should not participate in a premature b-scission step (Scheme 2). Finally, the transposed radical should possess a weak C À X bond which can undergo an efficient terminating b-scission step that renders the overall process irreversible, as shown in Scheme 2.…”