Formation of cyclic ethers via the palladium-catalyzed cycloaddition of activated olefins with allylic carbonates having a hydroxy group at the terminus of the carbon chain.
The reaction of the activated olefins 1 with the allylic carbonate 2, having a hydroxy group at the terminus of the carbon chain, in the presence of catalytic amounts of Pd(2)dba(3).CHCl(3) and dppe in THF at room temperature gave the corresponding cycloaddition products, tetrahydrofuran derivatives 5, in good to very high yields. The diastereoselectivities (trans/cis ratios) of the products were in the range of ca. 60-70/40-30. The reaction of 1 with the hydroxy allylic carbonate 3 in the presence of catalytic amounts of Pd(2)dba(3).CHCl(3) and (o-tolyl)(3)P in THF at 50 degrees C afforded the corresponding cycloaddition products, tetrahydropyran derivatives 6, in good to high yields. The trans/cis ratios of the products were in the range of ca. 0-40/99-80. The reaction of 1a with the hydroxy allylic carbonate 4 needed higher reaction temperatures (approximately 100 degrees C) to give the cycloaddition product, the oxepane 7a, in 31% yield with low diastereoselectivity. Next, catalytic asymmetric syntheses of tetrahydrofuran and -pyran derivatives were carried out. With the Trost ligand 15, good to high ees were accomplished in the cycloaddition, although the diastereoselectivities were of low level. With the Hayashi ligand 16, good to high ees were also achieved in the cycloaddition. The absolute stereochemistries of the major enantiomers of 5l, 5m, and 6d were determined unambiguously by X-ray crystallographic analysis: trans-(2R,4R)-5l, cis-(2S,4R)-5l, 4R-5m, trans-(2S,4S)-6d, and cis-(2R,4S)-6d were major enantiomers. Based upon the absolute stereochemistries of the major enantiomers, the mechanism of catalytic asymmetric induction in the cycloaddition reaction is discussed.
Sekido
M
M
Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan.
Aoyagi
K
K
Nakamura
H
H
Kabuto
C
C
Yamamoto
Y
Y