Chiral Phosphoric Acid Catalyzed "3+2" Cycloaddition And Kinetic Resolution Of 2,3-Allenoates

2.3-Allenoates have attracted organic chemists great interest due to their unique structure, facile preparation and diverse reactivity. Allenoates are very important building blocks for the synthesis of many natural products. biologically and pharmaceutically active molecules.In this dissertation, we established a chiral phosphoric acid catalyzed asymmetric 1. 3-dipolar cycloaddition of azomethine ylides involving 2,3-allenoates as dipolarophiles, yielding optically active 3-methylenepyrrolidine derivatives with excellent stereoselectivities (up to 97% ee) via screening of chiral phosphoric acids and variation of the substituent at the ester moiety of 2.3-allenoates. Interestingly, not only the enantioenriched pyrrolidine derivatives were obtained but also a kinetic resolution of 2.3-allenoates was observed via the bisphosphoric acid catalyzed 1.3-dipolar cycloaddition of racemic 2.3-allenoates with aromatic aldehydes and amino esters.Most of the reported methods for preparing optically active 2.3-allenoates require stoichiometric chiral resources as either substrates or reagents. Representative examples include chirality transfer from optically active centrally chiral propargyl compounds and stoichiometric enantioselective synthesis. However.few reports have described the organocatalytic asymmetric synthesis of chiralα-substituted 2.3-allenoic esters. After the optimization of the kinetic resolution reaction conditions was performed, it was found that the bisphosphoric acid was able to effectively resolve many racemicα-substituted 2.3-allenoates. In addition, the enantioenriched 2,3-allenoic esters obtained were applied to Diels-Alder reactions and the intermolecular cyclization, wherein the axial chirality of the 2,3-allenoates can be successfully transferred to the stereogenic center in the products. The X-ray structure revealed the assignment of the configuration of the resolved 2.3-allenoates to be R via the (R,R)-bisphosphoric acid catalyzed 1.3-dipolar cycloaddition.