Equatorial configuration

Neighbouring diaxial protons of cyclohexane can be clearly identified by their large coupling constants 11-13 Hz, Table 2.10) which contrast with those of protons in diequatorial or axial-equatorial configurations ( Jee 2-4 Hz). Similar relationships hold for pyranosides as oxy-... 

On the other hand, the NMR spectrum (Figure 6) of kasuganobiosa-mine (4) shows that the anomeric proton signal is located at 5.02 p.p.m., therefore the configuration of the proton is assigned to the equatorial configuration or the same ground (17,27). 

Van Leeuwen came to the conclusion that the equatorial/equatorial configuration in particular imposes a high linearity on the formed aldehydes [26-29]. Thus, the best selectivities to the linear aldehyde species should be obtained when the bite angle has a value of about 120°. The configuration of the ligand in equatorial/axial positions (bite angle 90°) leads to lower linearity of the formed aldehydes. 

C or N substituents on these five-membered puckered rings can be either axial or equatorial and the bulk of accumulated crystallographic evidence suggests that the equatorial configuration is favored47 for octahedral systems. Thus Co(NH3)4(R,S-pn)3 + should consist of equal amounts of Co(NH3 )4(R-pn-l)3+ and Co(NH3)4(S-pn-<5)3+ (14).,8S... 

The axial nature of the C-2 oxygen substituent was confirmed by its epimerization to the equatorial configuration. Treatment of methyldecinine... 

An X-ray study of vertaline hydrobromide established the structure and absolute stereochemistry of vertaline as shown in 51 (32, 43). The relative stereochemistry at C-l and C-3 in all alkaloids in the group is the same as in the biphenyl alkaloids for example, the biphenyl ether and lactone group are linked to the quinolizidine ring in axial and equatorial configurations, respectively. 

Epimerization of alpha-configuration of 10 into a p-equatorial configuration through acidic treatment and decomplexation by iodine provided the pseudo enantiomeric form of D-glucose derivative 11 (5). Finally, 11 is converted into the hetero olefin 12 which then received a variety of nucleophiles by chelation control to accomplish the synthesis of segment C of TTM 13. 

The stereochemistry of oxidation of 3-substituted thietanes has been discussed. Both thermodynamic and kinetic determination of products are observed. For example, oxidation of 3-t-butylthietane with dinitrogen tetroxide gives a cis trans ratio of 82 18 (the cis isomer is more thermodynamically stable than the trans, provided the sulfinyl oxygen prefers an equatorial configuration) whereas oxidation with hydrogen peroxide-acetic acid gives a cis trans ratio of 43 57. ... 

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