Enantioselective Synthesis Of Optically Active2,3-Allenoates From Propargyl Alcohols

Allenes are a class of compounds containing a cumulative diene functionality, which would be optically active when the two substituent groups on both of the terminal carbons of allene are different from each other. Among these,2,3-allenoates are an important type of fuctionalized allenes, which may undergo many reactions and have been becoming a type of very useful intermediates in organic synthesis. However, preparation of optically active2,3-allenoates is not well-established:harsh condition, low efficiency, high cost and limited substrate scope are the main drawbacks in known methods. Therefore, it is highly desired to develop new synthetic methods for optically active2,3-allenoates with high efficiency tolerating useful functional groups.This dissertation mainly focuses on the enantio selective synthesis of2,3-allenoates via Pd-catalyzed carbonylation from propargylic compounds with proper leaving groups, which can be easily prepared from propargyl alcohols in one step. Both chirality transfer from optically active substrates and catalytic chiral induction from racemic substrates are successfully developed:Part I:Chiral ligand-assisted high-pressure carbonylation of chiral propargylic mesylates. It is reported that optically active4-substituted2,3-allenoates can be prepared from optically active terminal propargylic mesylates with high chirality transfer efficiency using Pd(PPh3)4as the catalyst. However, the efficiency is rather low when non-terminal propargylic mesylates are used. We found that chiral ligand,(S)-Segphos, could successfully inhibit the racemization to afford optically active2,4-disubstituted2,3-allenoates in moderate to excellent yields with high chirality transfer efficiency.Part II:Non-chiral ligand-assisted high-pressure carbonylation of chiral propargylic mesylates. After further screening of the reaction conditions, we observed that the chirality transfer efficiency for the DPEphos-assisted high-pressure carbonylation is even higher. Furthermore, DPEphos is less expensive.Part III:Preparation of optically active2,3-allenoates via catalytic chiral induction from racemic propargylic carbonates. Pd-catalyzed carbonylation of propargylic carbonates proceeds even at room temperature and1atm of CO. After extensive study, we identified a new ligand,(R)-ECNU-Phos, for the effective enantioselective carbonylation leading to optically active2,3-allenoates.