Studies On The Synthesis Of 2,3-Allenoates

Allene is the common name given to hydrocarbons characterized by a cumulative diene functionality with two mutually perpendicular?-orbitals.This 1,2-diene structure has also been found in a variety of natural products and pharmaceutical molecules,and the unique axial chirality makes allene-containing chiral compounds applicable in asymmetric catalysis as catalyst or ligand.Besides,the unique chemical properties derived from this distinctive structure as well as the substituent-loading ability attributes to the broad application of allenes in the synthesis of natural products and pharmaceuticals.As an important class of functionalized allenes,2,3-allenoates are becoming significant building blocks in organic synthesis due to the versatile reactivity,which gives rise to ample interest in simple and efficient synthesis of2,3-allenoates,especially the optically active 2,3-allenoates.In this dissertation,we focused on the synthesis of 2,3-allenoates starting from propargylic alcohols,and the work can be divided into three parts:Part I:Palladium-catalyzed enatioselective synthesis of 2,3-allenoates from propargylic carbonates.Employing readily available differently substituted propargyliccarbonatesassubstrates,weidentified?R?-or?S?-3,4,5-?MeO?₃-MeOBIPHEP as the chiral ligand for a general highly enantioselective synthesis of optically active trisubstitued 2,3-allenoates with 90-98%ee.Comparing with the results applying?R?-or?S?-ECNU-Phos,an impressive improvement in enatioselectivity was observed.Functional groups such as ester,cyano,methoxy,and halogen are compatible in this transformation.Part II:Palladium/H⁺-catalyzed synthesis of 2,3-allenoates directly from propargylic alcohols.Applying propargylic alcohols as starting materials,a catalytic amount of Br?nsted acid was added for helping to cleave the propargylic carbon-oxygen bond.Subsequent reaction with CO and alcohol afforded multi-substituted 2,3-allenoates with moderate to excellent yields.In the primary screening of chiral ligands,?R?-DTBM-Garphos was able to accelerate the kinetic resolution process to obtain chiral allenoates with 84%ee,albeit with only 16%yield and 82%recovery of substrates;applying?R?-BTFM-Garphos may promote the yield to 83%,while the enantiomeric excess value was 63%.Part III:Palladium/H⁺-catalyzed kinetic resolution of tertiary propargylic alcohols aiming at the synthesis of 2,3-allenoates.A kinetic resolution reaction catalyzed by palladium and Br?nsted acid was realized recovering optically active tertiary propargylic alcohols with 90-98%ee,providing a new approach for the synthesis of such chiral alcohols.The obtained optically active alcohols may also be transferred into optically active tetrasubstitued allenoates without loss of enantiomeric excess.