Synthesis of Biologically Active Compounds Using Potential Utility of Transition Metals

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(1) Samarium(II) IodideMediated Spirocyclization onto an Aromatic Ring. Both the reduction and carboncarbon bond formation with samarium(II) reagents have attracted much interest in organic synthesis. In contrast, samarium(II) mediated radical cyclization onto an arene ring had been unprecedented until recently. In 2000, we found that a radical ipso substitution of the aromatic methoxy group is effectively promoted by samarium(II) to afford the cyclized products. Based on these results, the radical spirocyclization onto an aromatic ring have been realized starting from benzoate possessing an oxoalkyl group at the para position to the ester group (Chem. Commun. 2002, 316)(2) Development of PalladiumCatalyzed Sulfinylzincation. Sulfinyl anion is an important reaction intermediate to synthesize various sulfinyl compounds. We have firstly found that sulfinylzinc species can be generated upon treatment of 1 alkynyl suifoxides with Et_2Zn in the presence of Pd(0) catalyst (Org. Lett., 2001, 3, 3627). Owing to its easy generation under the very mild reaction conditions, this methodology enable to synthesize various functionalized vinylic suifoxides stereoselectively(3) Synthesis of Amino Allenes by a Novel PalladiumCatalyzed Reaction. Amino allenes have attracted considerable interest in recent years, since they are versatile substrates for constructing various azacycles. We found a general and efficient synthesis of allenes including amino allenes using a palladium(0)/diethylzinc system: treatment of mesylates or trichloroacetates of 2 bromoalk 2 en 1 ols with diethylzinc and a palladium(0) catalyst affords various allenes bearing an aminoalkyl, alkyl, or aryl substituent in good to high yields (J. Org, Chem. 2002, 67, 1359)