A Cycloaddition Forming Three-Membered Rings

You will become familiar with selected cycloadditions that lead to four-, five-, or six-mem -bered rings in Chapter 15. Here we only discuss the addition of dichlorocarbene (C12C) to olefins as an example of a cis-addition of the cycloaddition type. 

Dichlorocarbene cannot be isolated, but it can be produced in the presence of an alkene with which it rapidly reacts. The best dichlorocarbene precursor is the anion C13C , which easily eliminates a chloride ion. This anion is obtained from C13CH and fairly strong bases like potassium ferf-butoxide (KO-ferf-Bu), KOH or NaOH. The deprotonation of C13CH is run very efficiently with a solution of KO-terf-Bu in THF. Alternatively, when a concentrated aqueous solution of NaOH or KOH is vigorously stirred with a chloroform solution of the alkene (which is not miscible with the first) there is only moderate conversion into the corre- 

Side Note 3.1. The Principles of Phase Transfer Catalysis 

2 Additions to C=C Double Bonds That Are Related to Cycloadditions and Also Form Three-Membered Rings 

In contrast to the dichlorocyclopropanations from Section 3.3.1, the reactions discussed in this section are not cycloadditions in a strict sense. The reason is that the empirical formula of the addition products presented here is not equal to the sum of the empirical formulas of the reaction partners. 

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