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During the development of organic chemistry, five-and six-membered rings received the major share of systematic synthetic attention, and justifiably so. However, many organic substances of interest contain larger rings, and it has become important to explore and develop new avenues of approach to appropriately functionalized medium and large rings. Three general methods leading to the synthesis of medium rings havebeen outlined by Hesse in his outstanding recent monograph. 1® This review will emphasize two approaches: chain insertion (eq 1) and ring annulation (eq 2), both with bond cleavage. The focus of this review will be on recently developed free radical methods for ring expansion and related annu-lations. Ionic methods have an essential place inring expansion, and they have been well reviewed earlier by