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Ti-Catalyzed Barbier-Type Allylations and Related Reactions

机译：钛催化的Barbier型烯丙基化反应及相关反应

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摘要

TitanoceneACHTUNGTRENUNG(III) complexes,easily generated in situ from commercial TiIV precursors, catalyze Barbiertype allylations,intramolecular crotylations(cyclizations), and prenylations of a wide range of aldehydes and ketones.The reaction displays surprising and unprecedented mechanistic subtleties.In cyclizations a fast and irreversible addition of an allyl radical to a TiIII-coordinated carbonyl group seems to occur. Intermolecular additions to conjugated aldehydes proceed through a coupling of a TiIV-bound ketyl radical with an allyl radical. Reactions of ketones with allylic halides take place by the classical addition of an allylic organometallic reagent. The radical coupling processes enable transformations such as the highly regioselective a-prenylation that are otherwise difficult to achieve. The mild reaction conditions and the possibility to employ titanocene complexes in only catalytic quantities are highly attractive features of our protocol. These unusual properties have been taken advantage of for the straightforward synthesis of the natural products rosiridol, shikalkin, and 12-hydroxysqualene.
机译：钛茂ACHTUNGTRENUNG（III）络合物易于从商业TiIV前体原位生成，催化Barbiertype烯丙基化，分子内crotylations（环化）以及各种醛和酮的烯丙基化反应。似乎发生了将烯丙基不可逆地加到TiIII配位的羰基上的现象。共轭醛的分子间加成通过TiIV结合的酮基与烯丙基的偶联而进行。酮与烯丙基卤化物的反应是通过经典加入烯丙基有机金属试剂进行的。自由基偶联过程使诸如高区域选择性α-异戊二烯化的转化难以实现。温和的反应条件以及仅以催化量使用钛茂复合物的可能性是我们方案的极具吸引力的特征。这些非同寻常的性质已被利用来直接合成天然产物罗西多，罗奇金和12-羟基角鲨烯。

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