Axial/equatorial populations in ?-hetero-substituted cyclohexanone Oximes andO-methyl oximes

Abstract

Axial equatorial populations were determined for (E)‐2‐X‐cyclohexanone oximes and O‐methyl oxime ethers in chloroform by the Eliel method [X = F, Cl, Br, OCH3, N(CH3)2, SCH3]. A novel approach is presented, which uses 1H NMR data from the protons bonded to C‐6. The conformational proportions were also obtained from the C‐4 chemical shifts, the Z‐isomer spectral parameters being taken as reference for calculation. For both series, all substituents adopt preferentially the axial conformation (86– 96%), but the O‐methyl oxime ethers present an enhanced axial population compared with the corresponding oximes, owing to the accepted occurrence of a πC = NOH/σ*CX stabilizing interaction. Copyright © 2000 John Wiley & Sons, Ltd.

Stereochemical investigation of conjugate additions of carbon- and heteronucleophiles to ring-substituted nitrosocyclohexenes

“…A small amount (~10%) of the reductive dechlorination product of starting oxime 5a was also formed in this reaction. In addition, the major isomer 13a was found to be an inseparable 1:1 mixture of ( E/Z) -oxime geometric isomers 8 whereas the minor product 14a was exclusively ( E) as determined by X-ray analysis. Similar but improved stereoselectivity was observed in the conjugate addition reactions with aryl cuprates.…”

“…The configuration and chair conformation of 8a , as shown in Scheme 2, were established by NMR analysis. 8 Exposure of cis -α-chloro- O -silyloxime 5c 6a to the Denmark conditions in the presence of diethyl malonate potassium enolate (Method B) also afforded a comparable yield of the same trans -adduct 8a as the sole product. It seems reasonable that adduct 8a is formed in all three cases via preferred axial attack 9 on the half-chair conformation of 4- t -butylnitrosocyclohexene ( 7 ).…”

Formamido-Diterpenes from the South China Sea Sponge Acanthella cavernosa

“…The relative configuration of the decalin ring in 5 was the same as 12 , inferred from the chemical shifts of C-1 to C-10 and NOESY correlations of H-1/H-7, H 3 -20/H-6, and NH/H-1. A significant difference between 5 and 12 was found in the chemical shift of C-12 ( δ C 31.0 in 5 instead of δ C 38.2 in 12 ), which was caused by the γ-gauche effect [ 20 , 21 , 22 , 23 , 24 ], indicating an axial orientation of Cl–14. The relative configurations of C-7 and C-11 in 5 were determined as S * and R *, respectively, from NOESY correlations of H 3 -18/H-6, H 3 -18/H-8b, and H-8a/H-12, as shown in the Newman projection ( Figure 4 ).…”