Assessable Consequences of Through‐Bond Donor–Acceptor Interactions in β‐Aminoketones

Abstract

Reported are the syntheses of ester-functionalized (6-8) and alkyl-substituted (9) 1-aza-adamantanones; the easy handling of the compounds provides an opportunity to comprehensively study the fundamental changes in structure and reactivity that can accompany the donor-acceptor arrangement in rigid beta-aminoketones. X-ray structural analysis of trione 6 and dione 7 reveals bond length and angle variations consistent with through-bond (hyperconjugative) donor-acceptor interactions. Observed is a shortening of the C-N bond, elongation of the central C-C bond (to approximately 1.6 A), and a significant pyramidalization of the carbonyl carbon within the donor-sigma-acceptor pathway. UV/Vis spectra of 6-9 show a new absorption maximum (lambda(max)=260-275 nm in three solvents), the so-called "sigma-coupled transition"; the molar absorptivity scales with the number of carbonyl groups (for trione 6, epsilon approximately 3000, for dione 7, epsilon approximately 2000) and the band reversibly disappears upon addition of acid. IR and (13)C NMR spectroscopic data show trends consistent with through-bond donation to the carbonyl acceptor groups and commensurate weakening of the carbonyl pi bond. High yielding acid-mediated fragmentations are used to illustrate the effects of the donor-acceptor arrangement on the reactivity of the molecules. Given that donor-sigma-acceptor molecules have recently been found to show self-assembly behavior and macromolecular properties linked to their unusual structure, the current analysis encourages further consideration of the systems in advanced materials applications.

Selective and Sequential Aminolysis of Benzotrifuranone: Synergism of Electronic Effects and Ring Strain Gradient

“…Each successive aminolysis reaction converts one − OC(O)CH 2 − substituent to a less electron withdrawing − OH substituent 21 meta to the phenyl oxygen of a common lactone ring (−OH: σ I = 0.33, σ m = 0.12; − OAc: σ I = 0.42, σ m = 0.39 22 ). The increasingly downfield lactone carbonyl 13 C NMR resonances (Table 3, entry 1) and lower υ CO wavenumbers (Figure 2a and Table 3, entry 2) from BTF → 1b → 2bb (and BTP → 5b → 6bb) are consistent with this increase of electron density at the benzene ring based on spectroscopic trends known for meta-and para-substituted phenyl acetates. 14d,23 It further follows that the rate of aminolysis should progressively decrease, again given similar behavior observed upon introduction of electron-donating substituents (R 2 ) to phenyl acetates of the general structure p-R 2 PhOC(O)R 1 .…”

“…1 H NMR (500 MHz, DMSO-d 6 ) δ 9.52 (s, 1H), 9.30 (s, 1H), 8.11 (t, J = 5.7 Hz, 1H), 8.04 (t, J = 5.5 Hz, 1H), 3.02 (m, 4H), 2.77 (t, J = 7.2 Hz, 2H), 2.72−2.65 (m, 6H), 2.39 (m, 4 H), 1.35 (m, 4H), 1.28−1.14 (m, 16H), 0.84 (m, 6H). 13 75%). NMR data, recorded in DMSO-d 6 , is consistent with the structure of the compound.…”

“…The solution was then heated at 80°C for 2 h. The orange solution was concentrated under vacuo to give BTP (0.25 g, quant) as an off-white solid with no further purification required: 1 H NMR (500 MHz, DMSO-d 6 ): δ 2.94 (t, J = 7.3 Hz, 6H), 2.79 (t, J = 7.3 Hz, 6H). 13 Preparation of Representative/Model Compounds via Aminolysis. N-Benzyl-3-(5-hydroxy-2,8-dioxo-2,3,4,8,9,10hexahydropyrano[2,3-f ]chromen-6-yl)propanamide (5a).…”

Seven‐Membered Intramolecular Hydrogen Bonding of Phenols: Database Analysis and Phloroglucinol Model Compounds

“…Lastly, aromatic amide 5f shows the weakest H‐bond, a result not predicted by p K a values determined in water [i.e., N ‐methylacetamide (p K a = –0.6); acetanilide (p K a = 0.5)37]. The final entry in Table 6 includes known5d isopropyl acetate derivative 9 ; the δ OH value ( = 8.46 ppm) is consistent with the weak basicity of the ester carbonyl versus the amides of the other entries (i.e., isopropyl acetate p K a ≈ –3.542).…”

Tipping the balance: theoretical interrogation of divergent extended heterolytic fragmentations

“…28,46 These 1-aza-adamantane structures have played a signicant role in work done by the Castellano group in studying donor-acceptor through-bond interactions for crystal and materials design. [47][48][49] A simplied model system was designed such that it satised the expected structural and stereoelectronic requirements 50 for concerted fragmentation (1, Scheme 2). We hypothesized that this model system would undergo one of two possible concerted 7-atom fragmentations (red and blue arrows in Scheme 2).…”