Stereochemical course of addition

The remarkable sensitivity of the stereochemical course of addition to the constitution of the carbene within closely related groups of structures deserves detailed investigation. 

It has been demonstrated that 1 -phenyl-4- J-butyIcyclohexene is a very appropriate olefin for studying the stereochemistry of fluorination or halofluorination, where isomerization in the primarily formed cyclohexyl fluoro carbenium ion could be avoided by introduction of a J-butyl group67. Acid-catalyzed liquid-phase fluorine addition resulted in equal amount of cis and trans adducts, with the nature of the catalyst little influencing the stereochemistry, while introduction of a methoxy group into the phenyl ring also had no significant effect on the stereochemical course of addition (Scheme 18). 

In an examination of the stereochemical course of addition of phosphorodithioic acids to 1,2-unsaturated pento- and hexopyranoses, S-deuterated 0,0-dimethyl- and 0,0-bis(2,2-dimethyl-propyl) phosphorodithioates were prepared and reacted with D-glucal. These reactions were found to be fully stereoselective at both reaction centers C-l and C-2 and afforded S-D-ara-binopyranosyl phosphorodithioates 8 and 9 in quantitative yield deuterated at C-2 of the pyranosyl ring14. s... 

Nucleophilic additions to cyclic carbonyl compounds differ greatly from those of acyclic systems. In acyclic systems, only the configuration at an adjacent (1,2-asymmetric induction) or nea y center (remote asymmetric induction) is usually considered in predicting the outcome of nucleophilic attack. In cyclic systems, the conformation of the entire molecule (which is in part determined by the individual substituents) must be considered when predicting the mode of nucleophilic attack. Furthermore, a number of other factors such as torsional and electronic effects also play a role in the stereochemical course of additions to cyclic substrates. The relative importance of all of these effects (as well as others) has been the subject of considerable debate in the literature, and has not as yet been adequately resolved. ... 

Stereochemical course of addition oxidative metallation Relative stereoselection... 

Geometrical isomerism is a useful tool in investigating the stereochemical course of addition and elimination reactions. 

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