Development of Cationic Transition Metal Complex-Catalyzed Asymmetric [2+2] Cycloaddition Reaction

1.羰基化合物与乙烯酮的[2 + 2]环加成反应研究了几种阳离子8-10族过渡金属配合物催化的[2+2]环加成反应，其中钯、铂配合物表现出较好的催化性能。结果表明，催化剂的活性不仅受金属中心和配体的影响，还受抗衡阴离子的影响。利用手性配体诱导不对称反应的尝试失败了，但发现手性抗衡离子--取代BINOL衍生的四烷氧基硼酸酯在不对称反应中起到了手性识别元件的作用。2.串联[242]环加成-烯丙基重排或α，β-不饱和羰基化合物与烯酮的反应在α，β-不饱和羰基化合物的反应中，4-乙烯基氧杂环丁烷-2-酮经环加成反应重排生成3，6-二氢-2H-吡喃-2-酮。因此，一系列的α，β-不饱和醛和酮与乙烯酮的反应进行了检查，以推断重排的起源。发现如果在环加成中产生在乙烯基部分的4-位或2-位带有烷基取代基的4-乙烯基氧杂环丁烷-2-酮，则发生反应。在此基础上，提出了反应机理，认为反应中间体是4-乙烯基氧杂环丁烷-2-酮的C（4）-O键发生异裂而生成的两性环。通过使用在β-位带有不对称碳中心的α，β-不饱和醛，实现了高达57%的不对称诱导。3.刘易斯酸活化CO_2及其对碳-碳双键的化学固定作为本研究项目的延伸，研究了用铝基刘易斯酸活化CO_2并将其亲电固定到芳香族化合物和有机硅烷的可能性，这可能为将来由烯烃和CO_2制备氧杂环丁烷-2-酮提供一种新的方法。

1.[2+2] Cycloaddition reaction of carbonyl compounds with ketene The [2+2] cycloaddition reaction was examined by using some cationic group 8-10 transition metal complexes as the catalysts, among which palladiun and platinum complexes showed good perfonnance. It was found that the catalytic activity was greatly affected not only by the metal center and the ligand but also by the counter anion. Attempts on asymmetric induction by using chiral ligands failed but chiral counterions, tetraalkoxy borates derived from substituted BINOLs, were found to serve as a chirality-recognizing element in the asymmetric reaction.2.Tandem [242] cycloaddition-allylic rearrangement or α,β-unsaturatead carbonyl compounds with ketene In the reaction of α,β-unsaturated carbonyl compounds, 4-vinyloxetan-2-ones generated by the cycloaddition oflen rearrange under the conditions to give 3,6-dihydro-2H-pyran-2-ones. Thus, the reaction of a series of α,β-unsaturated aldehydes and ketones with ketene was examined to deduce the origin of the rearrangement. It was found that the reaction occurs if 4-vinyloxetan-2-ones bearing an alkyl substituent at the 4-position or at the 2-position of the vinyl moiety are generated in the cycloaddition. Based on the observations, a reacfion mechanism was proposed, which includes a zwitterion generated by heterolytic cleavage of the C(4)-0 bond of the 4-vinyloxetan-2-one as an intermediate. Asymmetric induction with up to 57% de has been achieved by using α,β-unsaturated aldehydes bearing an asymmetric carbon center at the β-position.3.Activation of CO_2 by Lewis acids and its chemical fixation to carbon-carbon double bonds As an extension of this research project, a possibility was examined to activate C0_2 by aluminum-based Lewis acids and fix it electrophilically to aromatic compounds and organosilanes, which might lead to an alternative method to prepare oxetan-2-ones from olefins and CO_2 in the future.