Conformational properties of cis,cis-1,4-cyclooctadiene. Dynamic nuclear magnetic resonance spectroscopy and iterative strain-energy calculations

Unexpected Vulnerability of DPEphos to C−O Activation in the Presence of Nucleophilic Metal Hydrides

“…Nucleophilic attack proceeds via TS(8-2) cct at + 25.0 kcal mol À1 ,w ith as hort H 1 •••C 1 distance of 1.56 and Ru•••H 1 stretching to 1.84 .T he C 1 ÀOb ond also lengthens to 1.48 and elongated C 1 ÀC 2 and C 1 ÀC 6 distances in the aryl ring suggestaMeisenheimer-type structure consistent with nucleophilic aromatic substitution. Hydride attack is also accompanied by ac onformational change in the 8-membered RuÀPÀC=CÀOÀC=CÀP ring, from ad istortedt wist-boat conformation in 8 cct to ab oat conformation in the transition state, [25] similar to the DPEphos fac-k 3 -P,O,P binding mode. [26] IRC calculations confirmt hat TS(8-2) cct links directly to 2 cct in which H 2 is trans to the phosphinophenolate oxygen.…”

Synthesis and Conformation of Chiral Eight-Membered 12H-Dibenzo[d,g][1,3,2]dioxaphosphocins1

“…Studies on the conformation of the 12 H -dibenzo[ d,g ][1,3,2]dioxaphosphocin ring have appeared only within the past 10 years. Quite recently, several reviews have appeared on the subject. ,− The commonly accepted nomenclature to describe the conformation of eight-membered rings is used herein; namely the boat−chair ( C s symmetry), boat−boat ( C s symmetry), twist-boat ( C 1 symmetry), and twist ( C 2 symmetry), which are abbreviated BC, BB, TB, and T, respectively. − Arshinova has noted that the boat conformer ( C 1 symmetry; abbreviated B) should also be considered as it is commonly found in the solid state. − The B conformation represents a highly distorted TB geometry about halfway between the symmetric C 2 T and BB geometries . The B conformation is characterized by a C aromatic −O−P−O torsion angle of 0° …”

Conformation and Absolute Configuration of Naturally Occurring Parvifoline and Several Synthetic Derivatives

“…-6076 (13) 3749 (5) 6755 ( 9.5 Hz, H-3' and H-5'), 8.34 (2H, 2mJortho = 9.5 Hz, H-2' and H-6'), 7.32 (1H, brs, H-4), 7.05 (1H, s, H-l), 3.80 (1H, s, H-14), 3.05 (1H, ddq,/8 9 = 7.0,y8 10 = 1.0,y8 lop= 10 Hz, H-8), 2.20 (3H,s, Me-7), 1.88 (1H, dddjlla,12a = 2.0,ynP-12a = 6.0,y12a-12P = 14 Hz,H-12a), 1.80(1H, ddt, y8iioa =1.0, yioa, ß -1?. yioa.na =yion.up = 4 Hz, H-lOa), 1.62 (2H, 2m, H-llct and H-11ß), 1.56 (3H, s, Me-15), 1.36 (1H, dddd,y8 10ß= 10 ,Jl0a 10p= 13,ylop ""= l,y10p,iip = 6 Hz, -10ß), 1.35 (3H, d,y8 9 = 7.0Hz, Me-9), and 1.19ppm(lH, ddd,yUal2p = 11.5,ynp,l2p = 2.5, Ji2tx 2ß = 13.5 Hz, -12ß); 13C nmr (75.4 MHz, CDC13) see Table 1; 13C-1H heteronuclear chemical shift correlation [75.4 (300 MHz), CDC13] 63.0 (3.80), 40.8 (1.80 and 1.36), 34.4 (3.05), 33.1 (1.88 and 1.19), 24.0(1.62), 22.1 (1.56), 22.0(1.35), 15.7(2.20).…”

“…Vicinal coupling constants and their corresponding calculated dihedral angles are given in , while approximate projections of the Dreiding models of 2, 5, 8, and 9 are drawn in Figures 1 to 4, respectively. According to published conformations for 1,3-and 1,4-cyclooctadiene (12,13) and for 1,3- 29.9(q) 29.8(q) 29.7(q) 29.4 (q) 15.......... In ppm from internal Me4Si.…”