Electronic versus steric control of ring-opening

In cyclic olefins, addition occurs by diaxial addition  

The addition of nitrosyl chloride to olefins is accompanied by subsequent reactions if the nitroso group is not tertiary. The nitroso compound may dimerize or rearrange to the more stable oxime tautomer. 

Hydrolysis of the nitrosyl chloride adducts can provide a convenient route to 

Q -chloroketones. Hydrolysis presumably proceeds via the oxime tautomer of the monomeric nitroso compound. Levulinic acid is used to react with the hydrox-ylamine formed in the oxime hydrolysis. The stereochemistry of nitrosyl chloride addition has not been investigated for a wide variety of olefins. Both syn and anti addition have been reported in systems studied to date. 

Phenylselenyl halides, phenylselenyl trifluoroacetate, and phenylselenyl acetate add to alkenes  

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Figure 3.2. Electronic versus steric control of ring-opening.

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