New Methodologies for Construction of Medium- and Large-sized Carbocycles

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The following synthetically useful methodologies have been developed by this research project.(1) The substrates such as 3- (alkylthio) -2- (siloxy) - and 3- (alkylthio) -2- (silylmethyl) allyl acetates have been shown as useful three carbon units for [3 + 2] cylopentanone and methylene cyclopentane annulation in the reactions with electron-rich olefins. It has also been proposed the high observed regioselectivity is due to thermodynamic control of this reaction, and excellent stereoselectivity observed in the reaction with vinylsulfides may be due to remarkable effect of sulfur having a largest HOMO coefficient. Based on this methodology, enantioselective total synthesis of coriolin has also been achieved.(2) Based on the remarkable feature of 3- (alkylthio) allylic acetates, construction of medium or large carbocycles has been examined by using substrates having appropriate olefinic moieties. Under the influence of appropriate Lewis acid, the reaction took place cleanly to afford the corresponding larger-sized carbocycles with almost complete regioselectivity.(3) For construction of a unique carbocycle of ingenol, a one step process involving cyclization followed by carbon skeleton rearrangement has been designed and examine. By using an appropriate Al reagent, the expected reaction proceeded nicely to give the product containing ingenane ABC-tricarbocycles. By utilizing the present methodology, synthetic studies on ingenol is in progress.