Cheng D, Zhu S, Yu Z, Cohen T
Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA.
J Am Chem Soc. 2001 Jan 10;123(1):30-4. doi: 10.1021/ja0029782.
The first example of a magnesium-ene cyclization stereochemically directed by an allylic oxyanionic group is demonstrated by a highly stereoselective synthesis of the bicyclic terpene matatabiether 10. The synthetic method is particularly valuable, not only because of the stereochemical control and the utility of the versatile hydroxyl group introduced into the product, but also because the precursor of the allylmagnesium is an allyl phenyl sulfide, which is more stable and more easily prepared in a connective fashion than the usual allyl halide precursor. Since the presence of lithium ions encourages undesirable proton transfer to the cyclized organometallic and is detrimental to the stereochemical control, the conversion of the allylic thioether to the allylmagnesium utilizes a lithium-free method involving direct reductive magnesiation in the presence of the magnesium-anthracene complex.
由烯丙基氧负离子基团立体化学导向的镁-烯环化反应的首个实例，通过双环萜类化合物马他他别醚10的高度立体选择性合成得以证明。该合成方法特别有价值，不仅因为其立体化学控制以及产物中引入的多功能羟基的实用性，还因为烯丙基镁的前体是烯丙基苯基硫醚，它比通常的烯丙基卤化物前体更稳定且更易于以连续方式制备。由于锂离子的存在会促使不期望的质子转移至环化的有机金属化合物并对立体化学控制不利，烯丙基硫醚向烯丙基镁的转化采用了一种无锂方法，该方法涉及在镁-蒽配合物存在下的直接还原镁化。
