Enantioselective Alkynylation of Aromatic Aldehydes Catalyzed by a Sterically Highly Demanding Chiral-at-Rhodium Lewis Acid

The enantioselective catalytic alkynylation of aromatic aldehydes is reported using a sterically highly hindered bis-cyclometalated rhodium-based Lewis acid catalyst featuring the octahedral metal as the only stereogenic center. Yields of 58–98% with 79–98% enantiomeric excess were achieved using 1–2 mol % of catalyst. This work complements previous work from our laboratory on the enantioselective alkynylation of 2-trifluoroacetyl imidazoles (Chem. - Eur. J. 2016, 22, 11977–11981) and trifluoromethyl ketones (J. Am. Chem. Soc. 2017, 139, 4322–4325) using catalysts with octahedral metal-centered chirality.本研究报道了以空间位阻极大的双环金属化铑基路易斯酸催化剂实现芳香醛的对映选择性催化炔基化反应，该催化剂以八面体金属作为唯一手性中心。在催化剂用量为1~2 mol%的条件下，产物收率可达58%~98%，对映体过量值（enantiomeric excess）为79%~98%。本研究补充了本课题组此前的相关工作：此前本课题组采用具有八面体金属中心手性的催化剂，分别完成了2-三氟乙酰基咪唑（Chem. - Eur. J. 2016, 22, 11977–11981）与三氟甲基酮（J. Am. Chem. Soc. 2017, 139, 4322–4325）的对映选择性炔基化研究。