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

1.羰基化合物与烯酮的[2+2]环加成反应采用阳离子基团8-10的过渡金属配合物作为催化剂，考察了[2+2]环加成反应，其中钯和铂配合物表现出较好的性能。结果表明，金属中心和配体不仅对催化活性有很大影响，反阴离子对催化活性也有很大影响。用手性配体诱导不对称反应的尝试失败了，但发现手性反离子——由取代的BINOLs衍生的四烷氧硼酸盐在不对称反应中起了手性识别作用。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在α，β-不饱和羰基化合物的反应中，由环加成生成的4-乙烯基-2-酮常在重排的条件下生成3,6-二氢- 2h -吡喃-2-酮。因此，研究了一系列α，β-不饱和醛和酮与烯酮的反应，以推断重排的起源。在环加成反应中，如果在乙烯基部分的4位或2位上有一个烷基取代基的4-乙烯基氧乙烷-2- 1就会发生反应。在此基础上，提出了一种反应机制，该机制包括4-乙烯基氯乙烷-2- 1的C(4)-0键的异裂裂解产生的两性离子作为中间体。利用α，β-不饱和醛在β-位置上带有一个不对称碳中心，实现了高达57%的不对称诱导。作为本研究的延伸，探讨了用铝基路易斯酸活化CO_2并将其亲电固定在芳香化合物和有机硅烷上的可能性，这可能为今后用烯烃和CO_2制备氧二酮提供一种替代方法。

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.