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This review deals with the development of efficient methods to construct the basic structure of natural products and the versatile methods to control the stereochemistry, and these methods were applied to the synthesis of natural compounds. The photochemical spirodienone formation reaction was applied to the synthesis of proaporphine alkaloids. The alternative spirodienone formation reactions by the metal-catalyzed degradation reaction of phenolic alpha-diazoketones were applied to many natural spirocyclic compounds, such as chamigrane type sesquiterpenes, spirovetivane type phytoalexins, marine natural products, and so on. Lewis acid mediated spirocyclization reaction of cyclohexene bis-acetal derivative was developed, and this reaction was applied to the synthesis of aphidicolane and stemodane diterpenes. The regioselective cleavage reaction of the cyclopropane ring of tricyclooctanone derivatives was used for the syntheses of diquinane and triquinane compounds. A chiral pool synthesis of several aromadendrane sesquiterpenes was achieved via common tricyclic enone intermediates. The synthesis of macrocarpals, coupling products of aromadendrane skeleton and isopentylphloroglucinol dialdehyde, was also accomplished for the first time using an arene Cr(CO)3 complex as a chiral benzyl cation equivalent. The Fe(diene)(CO)3 complexes were used for the highly stereoselective asymmetric synthesis of several natural products, such as insect pheromones and alkaloid, as a versatile mobile chiral auxiliary.

Several novel reactions utilizing the latent feature of sulfur atoms have been developed. We found that chiral p-toluenesulfinyl groups on olefines control the stereochemistry in highly diastereoselective manners as show in the following three types of reactions: 1) intramolecular Michael addition reactions, 2) Pummerer-type reactions, and 3) cyclopropanation reactions. These chiral auxiliary groups are also very efficient for the asymmetric desymmetrization of sigma-symmetric diols via diastereoselective acetal fission. In addition, it was revealed that an aryl sulfide group on the cyclopropyl ring triggers single electron transfer reactions via cation radical species, resulting in the following reactions: 1) tandem oxidative ring cleavage-cyclization reactions and 2) intramolecular [3 + 2] cycloaddition reactions. These reactions have been applied to the syntheses of natural products.