Ring-opening reactions of oxetanes include nucleophilic, electrophilic, radical, acid-catalyzed, and reductive ring-opening modes. Ring-opening reactions of unsymmetric oxetanes and their regioselectivity are summarized and reviewed. The regioselectivity of these ring-opening reactions is mainly influenced by steric and electronic effects. Nucleophilic ring-opening reactions of unsymmetric oxetanes with various nucleophiles are major ring opening reactions of oxetanes. Strong nucleophiles mainly attack the less substituted oxygen-adjacent carbon atom of unsymmetric oxetanes (steric effect control). They attack on the β-carbon atom of the vinyl group in 2-vinyloxetanes, undergoing an S_N2' ring-opening reaction. Only in the presence of acids, unsymmetric oxetanes can be attacked on their more substituted oxygen-adjacent carbon atom with weak nucleophiles such as O-nucleophiles or halides (electronic effect control). However, electrophilic ring-enlargement reactions, radical ring-opening coupling reactions, Lewis acid-catalyzed ring-opening reactions and Pd-catalyzed hydrogenolysis reactions take place at sterically hindered oxygen-adjacent carbon atom of unsymmtric oxetanes. The current summarized results provide important and useful imformation for chemists who apply ring-opening reactions of oxetanes and promote the application of ring-opening reactions of oxetanes.

Contents
1 Nucleophilc ring-opening reactions
1.1 Nuclephiles in group C
1.2 Nucleophiles in group N
1.3 Nucleophiles in group O
1.4 Halogen nucleophiles
1.5 Hydride nucleophiles
2 Electrophilic ring-enlargement reactions
3 Radical ring-opening coupling reactions
4 Miscellaneous ring-opening reactions
4.1 Strong base-promoted ring-opening reactions
4.2 Lewis acid-catalyzed ring-opening reactions
4.3 Acid-catalyzed ring-opening and ring enlargement reactions
4.4 Reductive ring-opening reactions
5 Conclusions