Synthesis of an antitumor active chelerythrine type alkaloid using Claisen rearrangement of a propargyl ether

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1. Claisen Rearrangement of Aryl Propargyl Ether in the Presence of CsF: We found that Claisen rearrangement of the propargyl ether (1) in the presence of CsF , easily prepared, gave only the furan (3) but not the pyran (2) . This new reaction was examined in detail using the -naphthol derivative (4). The following facts were found on formation of a furan ring: (a) The best solvent was PHNET_2. (b) Other additives ex-cept CsF could not act. (c) A catalytic amount of CsF was enough, but practically about equimolar amount of it was needed. Heating 5__-, 6__- and the acetal of 7__- in PhNEt_2 containing CsF gave the corresponding furans in good yields, respectively, indicating generality of the reaction.KA2. Cleavage of the Furan Ring: The furan (8) derived from 7__- was used as a model compound for cleavage reaction of a furan ring. Successive treatment of 8__- with a stoichiometric amount of OsO_4, NaIO_4, and dil. NaHCO_3 aq. provided the desired salicylaldehyde (9) in satisfactory yield.3. Synthesis of Chelerythrine (11): The aldehyde (10) was prepared from 3__- using the method mentioned adove. Treatment of the methyl ether of 10__- with TsOH resulted in deprotection and cyc-lization to give chelerythrine (11). We succeeded in synthesizing a chelerythrine type alkaloid.KA