Stereocomplementary Routes to Hydroxylated Nitrogen Heterocycles: Total Syntheses of Casuarine, Australine, and 7‐<i>epi</i>‐Australine
書誌事項
- 公開日
- 2013-07-04
- 権利情報
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- http://onlinelibrary.wiley.com/termsAndConditions#vor
- DOI
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- 10.1002/chem.201301320
- 公開者
- Wiley
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説明
<jats:title>Abstract</jats:title><jats:p>Addition of lithiated 1‐benzyloxyallene to a <jats:sc>D</jats:sc>‐arabinose‐derived cyclic nitrone occurred with perfect diastereoselectivity furnishing a bicyclic 1,2‐oxazine derivative, which is an excellent precursor for pyrrolizidine alkaloids hydroxylated at C‐7 with optional configuration at this stereogenic center. Depending on the stage of the NO bond cleavage and ring re‐closure, 7‐hydroxypyrrolizidines with 7<jats:italic>R</jats:italic> or 7<jats:italic>S</jats:italic> configuration were obtained, as a result of completely selective addition reactions occurring complementarily at the bottom or top face of the endocyclic CC double bond in six‐ and five‐membered B rings, respectively. Applicability of these stereodivergent routes to obtain polyhydroxy pyrrolizidine alkaloids is demonstrated by the efficient syntheses of casuarine and australine as examples of the two classes of diversely configured 7‐hydroxypyrrolizidine alkaloids. An alternative synthesis of australine and two strategies for the preparation of 7‐<jats:italic>epi</jats:italic>‐australine are also reported, which demonstrate that the stereoselectivity of hydride reduction of an exocyclic CO double bond is independent of the ring size, occurring preferentially from the top face either in a six‐ or five‐membered ring.</jats:p>
収録刊行物
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- Chemistry – A European Journal
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Chemistry – A European Journal 19 (32), 10595-10604, 2013-07-04
Wiley
