Four-membered ring systems oxetanes

The copolymerization with CO2 is a general reaction for epoxides unsubsti tuled, munosubstituted and disubstituted epoxides, such as propylene oxide or cydohexene oxide, are readily copolymerizable. Four membered ring ethers (oxetanes) or five membercd ring ethers (tetrahydrofuran), however, do not copolymerizc in the presence of the organozinc catalyst system. 

Closure of the biradical leads to a four-membered ring containing oxygen, which is known as an oxetane. The overall 1,2-photocycloaddition reaction is often called the Patemo-Biichi reaction (equation 12.60). The Patemo-Biichi reaction provides synthetic entry into highly strained ring systems containing oxygen atoms, as exemplified by equations 12.61 and 12.62 (where Ar is 2-naphthyl). ... 

Cyclic ethers can be named in several ways. One simple way is to use teplacement nomenclature, in which we relate the cyclic ether to the corresponding hydrocarbon ring system and use the prefix oxa- to indicate that an oxygen atom replaces a CH2 group. In another system, a cyclic three-membered ether is named oxirane and a four-membered ether is called oxetane. Several simple cyclic ethers also have common names in the examples below, these common names are given in parentheses. Tetrahydrofuran (THF) and 1,4-dioxane are useful solvents ... 

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