Reactions between enaminones and enones. Part 2. C versus N-Alkylation with cyclohex-2-enone. Structure confirmation by reduction of a dienaminone derivative of dehydrated dimedone dimer

Abstract

Primary and secondary enaminones derived from cyclohexane-l,3-dione, dimedone, and acetylacetone react with cyclohexenone to give exclusively C-alkylated derivatives. In every case the products form carbinolamines which exist as 1hydroxy-2-azacyclo [3.3.1] nonenes. This was confirmed in some examples by formation of an extra ring between nitrogen and oxygen. A series of dienaminones were prepared from 2-(5,5-dimethyl-3-oxocyclohex-

Tetronamides as Latent Acyclic Vinylogous Amides in Formal Aza-[3 + 3] Cycloaddition Reactions with α,β-Unsaturated Iminium Salts. An Unexpected Rearrangement and an Approach to Synthesis of Substituted Piperidines

“…An alternative pathway from 28 would involve an intramolecular S N 2‘ addition followed by an appropriate tautomerization. These assessments are in accord with those described in Hickmott−Stille's aza -annulation. −

4 Mechanistic Model for the Regioisomer

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“…Annulations of vinylogous amides with α,β-unsaturated iminium salts provide a convergent and practical approach for synthesis of alkaloids. , The formation of six-membered nitrogen heterocycles 3 [Figure ] constitutes a formal aza -[3 + 3] cycloaddition − because two of the five carbons along with the nitrogen atom originate from vinylogous amides 1 with the remaining three carbons from the α,β-unsaturated iminium salts . Specifically in our studies, α,β-unsaturated iminium salts 2 have been employed to afford exclusively 1,2-dihydropyridines 3 in a highly regioselective manner [Figure ]. − The regiochemistry of our reactions is opposite from that of Hickmott−Stille's aza -annulation using acid anhydrides or chlorides. − Mechanistically, we demonstrated that they proceed through a 6π-electron electrocyclic ring-closure of 1-azatrienes 4 7a,b,14,15 [derived from a Knoevenagel condensation], a process that can be rendered highly diastereoselective. 7a,15a,

1 Overview of the formal [3 + 3].

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Isolation of Fluorescent Benzoxazines with Neuroprotective Activity from the Olive Weevil Pimelocerus perforatus

“…The IR absorption bands at 3405, 1653, 1626, 1569, 1542, and 1517 cm –1 suggested the presence of OH, NH, CO, and CC functionalities. The UV (MeOH) absorption maxima at 260 (log ε 3.65) and 342 nm (log ε 3.98) (Figure ) implied the presence of a β-enaminone chromophore, − which was supported by the 1 H and 13 C NMR data [δ H 5.55 (1H, s, H-6); δ C 191.4 (C-5), 159.0 (C-6a), and 98.4 (C-6)] (Table ). The COSY and HMQC spectra also revealed the presence of a trisubstituted benzene ring [δ H 6.87, 6.88, and 6.89 (each 1H, overlap, H-8, 9, 11); δ C 116.7 (C-8), 119.1 (C-11), 125.2 (C-7a), 124.6 (C-9), 137.3 (C-10), and 144.3 (C-11a)], aliphatic methylene [δ H 2.19 (1H, d, J = 11.4 Hz, H-13 ax ), 2.38 (1H, dd, J = 11.4 and 2.3 Hz, H-13 eq ); δ C 44.8 (C-13)], and two hydroxyethyl groups [δ H 1.73 (1H, ddd, J = 12.8, 11.9, 6.0 Hz, H-1 ax ), 1.76 (1H, br d, J = 12.8 Hz, H-1 eq ), 2.75 (2H, t, J = 6.9 Hz, H-14), 3.55 (1H, ddd, J = 11.9, 11.9, 4.1 Hz, H-2 ax ), 3.72 (2H, t, J = 6.9 Hz, H-15), and 4.03 (1H, ddd, J = 11.9, 6.0, 1.4 Hz, H-2 eq )].…”

3-Amino-5,5-dimethylcyclohex-2-enone in the synthesis of heterocyclic compounds (review)

“…Boiling of equimolar amounts of compound 1 and cyclohexenone in propionic acid for 1 h leads to the formation of the hydroxyazatridecenone 111. This is only possible as a result of the initial C-alkylation with the formation of the intermediate 110 [61]. The reaction of compound 1 with ninhydrin leads to the formation of 4b,9b-dihydroxyindeno-[1,2-b]indole 116 [63].…”