Novel Organic Syntheses by Reconstruction of Carbon Skeletons via Catalytic Carbon-Carbon Bond Cleavage

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The catalytic cleavage of C-C bonds has been one of the most difficult challenges in the fields of organic and organometallic chemistry. This chemistry has recently received much scientific and technological interest, and has opened the door to a new field of synthetic organic chemistry. The next challenging subject is the reconstruction of new carbon skeletons after C-C bond cleavag, leading to the rapid and selective synthesis of novel organic molecules which can not be obtained by the simple combination of traditional synthetic methods. Among our recent reports on the ruthenium-catalyzed C-C bond cleaving reactions, the theoretical study for mechanism on the selective deallylation of tertiary homoallyl alcohols involving β-carbon elimi nation was first carried out. Then, we focused our attention on the reactivity of cyclopropenones and cyclobutenones which are the suitable strained organic molecules for C-C bond cleavage. After many trials, we developed an unprecedented ruthenium-catalvzed carbonylative dimerization of cyclopropenones involving C-C bond cleavage, which gave a novel organic functional monomer, pyranopyrandiones, in high yield. Furthermore, cross-carbonylation of cycloprorenones with alkynes was also found to give unsymmetrically substituted pyranopyrandiones. On the other hand, novel ruthenium-catalyzed dimerization of cyclobutenones to 2-pyranones has also been developed. This reaction may proceed via an η4-vinylketene intermediate, The reaction was also catalyzed by some rhodium complexes, however, the stereochemistry of the external alkenyl-substituent is totally different between the reactions using ruthenium (Z rich) and rhodium (E rich) catalysts.