P-8 Rh(I)触媒によるカスケード型環化反応を利用した多環式化合物合成法の開発(ポスター発表の部)

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We have recently reported a novel Rh(I)-catalyzed cascade reaction by combination of a hydroacylation of 4,6-dienal and a cycloisomerization of the resultant triene, giving a bicyclo[5.3.0]decenone derivative (Scheme 1). By the use of the cascade reaction, the synthesis of (±)-epiglobulol has been also accomplished. Herein, we report the construction of polycyclic compounds using the Rh(I)-catalyzed cascade reaction with the aim of the synthesis of Guanacastepenes (Scheme 2). Treatment of syn-3 with 10 mol% of [Rh(dppe)]ClO4 in dichloroethane at 65 ℃ for 6 h gave the desired tricyclic compound syn-4 in 34% yield along with syn-S, anti-4, and anti-5 in 8%, 7%, and 23% yields, respectively (Scheme 3). It was thought that bicyclic compound syn-5 was formed through reductive elimination from 6 (Scheme 4). On the other hand, anti-4, and anti-5 should be produced from anti-3, which would be formed from syn-3 via epimerization of a-proton of the aldehyde moiety syn-3. In the cyclization of anti-3 under the same conditions, bicyclic compound anti-5 was produced as the major product in 32% yield and the desired tricyclic compound anti-4 was produced in only 9% yield. These results indicate that the stereochemistry of cyclohexane ring in 3 affects on the reaction course. In order to prevent the isomerization of syn-3 to anti-3, the reactions of syn-3 were examined under the various conditions (Table 1). It was found that the cyclization of syn-3 in the presence of MS 4A gave the cyclized product syn-4 in 61% yield as the major product, while anti-4 and anti-5 derived from anti-3 were not obtained.
天然有機化合物討論会の論文
2007-08-24

P-8 Rh(I)触媒によるカスケード型環化反応を利用した多環式化合物合成法の開発(ポスター発表の部)

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