Oxa Bowls:  Synthesis of New Tetraoxa-Cages and Their C−H···O-Mediated Solid-State Architecture

Abstract

We have envisioned a new family of oxa-bowls, and a general approach to these entities has been proposed through polycyclic frameworks having two converging olefinic double bonds. Ozonolysis of such molecules was envisaged to give all-cis-tetraaldehyde functionality, which could undergo intramolecular cascade acetalization to oxa-bowls having C(2)(v )()symmetry. Homohypostrophene 16a and its functionalized derivative 16b and hypostrophene 17 on ozonolysis furnished the oxa-cages 22a, 22b, and 23, respectively. Single-crystal X-ray analysis of 22a and 23 showed an interesting network of C-H.O interactions mainly involving the nonacidic cycloalkane hydrogen atoms. The molecule 22a exhibits an interesting tapelike C-H.O hydrogen bonding motif in its crystal structure. On the other hand, the molecule 23 revealed an undulated ribbonlike C-H. O motif. The "chain of rings" pattern of C-H.O interactions in 23 has been observed for the first time in the solid-state structure of oxa-bowls.

Cooperative Effect of a Classical and a Weak Hydrogen Bond for the Metal‐Induced Construction of a Self‐Assembled β‐Turn Mimic

“…also show an AB system with a typical 2 J P,P coupling of [13][14][15][16] Hz, which confirms the presence of two non-equivalent phosphane ligands coordinated to the same platinum centre. [34] Moreover, the 1 J Pt,P coupling constant greater than 3650 Hz is in the order expected for a cis-Pt II diphosphane complex.…”

“…81 8C (CH 2 Cl 2 ); 1 H NMR (400 MHz, CDCl 3 ): d = 6.98 (dd, J = 6.8, 1. 4 Hz,1 H;ArH),12 H;ArH); 13 3.83, N 4.09; found: C 59.47, H 3.90, N 4.26. nBuLi (2.60 mL, 3.47 mmol, 1.1 equiv, 1.35 m in hexanes) was added dropwise to a solution of 6-diphenylphosphanyl-2-bromopyridine (1.081 g, 3.159 mmol) in dry THF (40 mL) at À110 to À100 8C and stirred at that temperature for further 0.5 h. Then CO 2 gas was bubbled through the reaction mixture for 0.5 h and the colour changed from orange-red to yellow.…”

“…The resulting white, chalky solution was stirred at room temperature for a further 16 h. The mixture was filtered through a 2 cm pad of Celite (wetted with CH 2 Cl 2 ), and the filter cake was washed with some CH 2 Cl 2 . After concentration in vacuo, the residue was subjected to chromatography on silica gel (PE/EE, 3:1) to afford the dipeptide ligand 4.30 (dd,J = 8.8,6.7 Hz,1 H;4.51 (dd,J = 8.6,4.8 Hz,1 H;6.49 (d,J = 8.6 Hz,1 H;11 H;ArH),7.73 (ddd,J = 7.8,7.8,2.2 Hz,1 H;8.05 (d,J = 7.8 Hz,1 H;8.13 ppm (d,J = 8.8 Hz,1 H;; 13 C NMR (100 MHz, CDCl 3 ): d = 17.9, 18.0, 19.0, 19.6 (C 4 , C 5 , C 9 , C 10 ), 30.0, 31.2 (C 3 , C 8 H 6.60, N 8.09; found: C 66.88, H 6.73, N 8.02.…”

“…[7] In the past few years, the main interest in the investigation of hydrogen-bond-assisted self-assembly in the solid and solution state was concentrated on heteroatom X À H···Y hydrogen-bonding-directed self-organisation with a strong hydrogen donor. [10][11][12] Besides these well known, comparably strong hydrogen bonds, only a few examples of CÀH···X hydrogen bonds are described in the formation and stabilisation of self-assembled structures both in the solid state [12][13][14][15][16] and in solution. [6f, g, 15a, b] To the best of our knowledge, molecular recognition through weaker hydrogen bonding has not been employed for the directed construction of supramolecular systems in solution, although this unusual interaction Abstract: A novel metal-induced template for the self-assembly of two independent phosphane ligands by means of unprecedented multiple noncovalent interactions (classical hydrogen bond, weak hydrogen bond, metal coordination, p-stacking interaction) was developed and investigated.…”

“…M.p. 145 8C (MeOH); 1 H NMR (400 MHz, CDCl 3 ): 10 H; ArH), J = 7.7 Hz, 2 H; ArH), ppm (m, J = 8.2 Hz, 2 H; ArH);13 C NMR (100 MHz, CDCl 3 ): d = 128.7 (d, J C,P = 5.8 Hz; C 5 ), 128.8 (d, J C,P = 7.2 Hz; 4ArC meta ), 129.1 (2ArC para ), 129.7 (d, J C,P = 6.9 Hz; C 1 ), 130.5 (C 6 ), 133.8 (d, J C,P = 19.9 Hz; 4ArC ortho ), 135.6 (d, J C,P = 22.2 Hz; C 2 ), 136.5 (d, J C,P = 10.7 Hz; 2ArC ipso ), 138.7 (d, J C,P = 13.8 Hz; C 3 ), 138.8 (d, J C,P = 17.6 Hz; C 4 ), 171.7 ppm (C=O);31 P NMR (162 MHz, CDCl 3 ): d = À5.23 ppm (s); HRMS (EIMS): m/z: calcd for C 19 H 15 O 2 P: 306.0809 [M + ]; found: 306.0803; elemental analysis calcd (%) for C 19 H 15 O 2 P: C 74.50, H 4.94; found: C 74.35, H 5.05.3-(Diphenylphosphanyl)benzoic acid methyl ester (3 a): Dicyclohexylcarbodiimide (DCC) (0.135 g, 0.653 mmol, 1.0 equiv) was added to a solution of m-DPPBA (2) (0.200 g, 0.653 mmol) and DMAP (8.8 mg, 0.07 mmol, 0.1 equiv) in dry MeOH (2 mL) at room temperature. The resulting white, chalky solution was stirred at room temperature for further 3 h. The mixture was filtered through a 2 cm pad of Celite (wetted with CH 2 Cl 2 ), and the filter cake was washed with some CH 2 Cl 2 .…”