Several criteria for the measure of synthetic strategies toward "ideal synthesis" are available to guide the design. and evaluation of the synthetic strategies toward the target molecules. One strategy toward "ideal synthesis" is developing a multistep reaction that involves dramatic change in complexity. Biogenesis of natural products and mechanistic investigation of complicated organic transformation provide good inspiration for design of new synthetic strategies. Trimethylenemethane diradical (TMM diyl), first introduced only as a theoretically interesting structure 60 years ago, gained interests of physical organic chemistry when it was first detected by Dowd. Study of characteristics and properties of TMM diyl was accelerated in a great deal when Koebrich observed dimeric hydrocarbon products from the reaction of 1,1-dibromo-2-methylhexa-1,5-diene with MeLi. Berson followed the mechanistic investigation of the reaction that involved 2-methylenecyclopentane-1,3-diyl, and thoroughly studied physical and chemical properties of the TMM diyl. This lead to the development of intramolecular [2 + 3] TMM diyl cycloaddition reaction for the construction of linearly fused triquinanes by Little.