Direct synthetic method for preparation of organotitanium complexes and their synthetic utility

由于缺乏一种实用的合成方法，利用钛(II)络合物进行有机合成一直没有得到探索。最近，我们发现，Ti(O-i-Pr)_4与2当量的i-PrMgX反应，得到了实质上定量产率的(eta^2-丙烯)Ti(O-i-Pr)_2(1)，它是一种多功能的钛(II)当量化合物。我们现在揭示了以下合成上有用的反应：1.1)环烯丙基化合物与1的反应提供了相应的环烯丙基钛络合物，它反过来与醛和亚胺发生高度立体选择性的反应。2)1)与不饱和的酯或碳酸酯的反应导致分子内的酰基取代反应，从而开辟了包括N-杂环在内的新的环状化合物。3)1)与炔烃反应得到钛-炔基络合物，后者又与光学活性的醛反应，以手性形式立体选择性地仿射烯丙醇。4)烯丙基碳酸酯的分子内酰基取代为合成具有光学活性的化合物提供了一种新的方法

Organic synthesis using titanium (II) complexes has remained unexplored because of the lack of a practical method for synthesis of them. Recently, we have found that the reacition of Ti (O-i-Pr)_4 with 2 equivalent of i-PrMgX provides (eta^2-propene) Ti (O-i-Pr)_2 (1) in essentially quantitative yield and it acts as versatile titanium (II) equivalent. We have now revealed the following synthetically useful reactions using 1.1) Reaction of cyclic allylic compounds with 1 provides the corresponding cyclic allyltitanium complexes, which in turn react with aldehydes and imines highly stereoselectively.2) Reaction of 1 with unsaturated esters or carbonates results in intramolecular acyl substitution reaction, thus opening up a new entry cyclic compounds, including N-heterocycles.3) 1 reacts with alkynes to afford titanium-alkyne complexes which in turn react with optically active aldehydes stereoselectively afforeling allylic alcohols in chiral form.4) Intramolecular acyl substitution of allenylic carbonates affords a new methodology for synthesizing optically active compounds