From five-membered rings

Carbon dioxide is readily extruded from five-membered rings, by thermolysis or photolysis (Scheme 28). 

Zeolite Socony Mobil constructed from five-membered-ring building units... 

Two other syntheses starting from five-membered rings are shown in Equations (103) <1978LA473> and (104) <1999CHE866>. 

Elimination of a One Ring-Atom Fragment from Five-Membered Rings... 

Synthesis of Six-membered Rings from Other Heterocycles 4.2.4.3.1 From five-membered rings... 

By formation of seven- from five-membered rings The formation of the oxepanes (160) and (161) by treatment of 2,2,5,5-tetramethyl-tetrahydrofuran-3-one with diazomethane is included in the present category although it is probable that the reaction proceeds by two separate ring expansion steps (cf. equation 47) as shown in Scheme 32 (72HC(26)l). Photolytic C—O bond cleavage of a dihydrofuran... 

By formation of seven- from five-membered rings The mechanism of thermal isomerization of the cyclobutene compound in equation (74) to thiepin (50) is directly analogous to that found in the synthesis of dihydrothiepins (221) and (222 equation 65). Compound (50) was the first monocyclic thiepin to have been identified (74T2093). This synthetic route has also been applied to thiepin (148) (74T2431). 

Ring contraction of heterocycles by sulfur extrusion including a chapter on four-membered rings from five-membered rings was recently reviewed by Bohle and Liebscher [96AHC(65)39]. 

By formation of seven- from five-membered rings 75... 

From five-membered ring heterocycles with one heteroatom 938... 

From five-membered rings Synthesis of pyrene derivatives from five-membered ring precursors by ring enlargement [13]. 

---