TADDOL-Derived Cationic Phosphonites: Toward an Effective Enantioselective Synthesis of [6]Helicenes via Au-Catalyzed Alkyne Hydroarylation

A series
of cationic phosphonites, all sharing a TADDOL skeleton
but decorated with different positively charged substituents at phosphorus,
were synthesized and tested as chiral ancillary ligands on the Au-catalyzed
intramolecular hydroarylation of appropriate diynes toward carbo[6]­helicenes
with different substitution patterns. Our studies showed that the
Au complexes derived from phosphonites bearing 1,3-dimesityl-1,2,3-triazolium
and 1,4-dimesityl-1,2,4-triazolium substituents are the best precatalysts
for the desired cyclization in terms of regio- and enantioselectivity
of the products obtained. In contrast, all of our attempts to prepare
Au complexes from cationic phosphonites derived from CAACs failed,
and only ligand decomposition products could be isolated.

本研究合成了一系列共享TADDOL骨架、在磷原子上修饰有不同带正电取代基的阳离子亚膦酸酯，并将其作为手性辅助配体，应用于金催化的合适二炔类化合物经分子内氢芳基化反应合成不同取代模式碳[6]螺烯的反应中开展性能测试。研究结果表明，带有1,3-均三甲苯基-1,2,3-三氮唑鎓与1,4-均三甲苯基-1,2,4-三氮唑鎓取代基的亚膦酸酯所衍生的金配合物，在所得产物的区域选择性与对映选择性方面，是目标环化反应的最优预催化剂。与之相反，本团队所有以环烷基氨基卡宾（CAAC）衍生的阳离子亚膦酸酯制备金配合物的尝试均告失败，仅能分离得到配体分解产物。