The Synthesis Of The Optically Pure 1,4-dienylboronates Through Copper-Catalyzed Chirality Transfer

Boron-substituted 1,4-dienes are versatile building blocks for the synthesis of 1,4-dienes(skipped alkenes),because of their utility in the Suzuki-Miyaura coupling reaction and conjugate additions.A method for the synthesis of boron-substituted1,4-dienes by means of copper-catalyzed boryl-allylation of alkynes with allyl phosphate and bis(pinacolato)diboron has been developed.The synthesis of optical activity products is very valuable.So on the basis of previous research work we use chiral substrates to get 1,4-dienylboronates via chirality transfer.The following results:(1)Synthesis of optically active vinyl phosphateWe have obtained the optically pure propargylic alcohols,which have shown excellent enantioselectivity in Ru-catalyzed hydrogenation of acetylenic ketones.The products are reduced to Z-optically pure allyl alcohol via the Ni/H2 way.Then the above react with chloride phosphate to get the final allyl phosphate.The ee of the products are often gteater than 96%.(2)Establishment of enantiomers analysis methodBecause the polarity of 1,4-dienylboronates is low,we can't use the commom chiral column to analyze the optical purity of the products directly by HPLC.So the 1,4-dienylboronates coupled with halogenated hydrocarbon.Tnen the disubstituted double bond was oxidized to aldehyde by ozone and in the reduction of aldehydes into ?-chiral alcohols with NaBH4.It is more convenient for the analysis.(3)The optimized Chirality migration conditionsAccording to the further temperature adjustment and ligands screening,we confirmed the best reaction condition.Temperature was 50 °C and ligand was Xphos.Thus the ee of the products increased to 92% gradually.(4)The expansion of the substrateWnen the ?-and ?-substituents of allyl phosphate were changed,there exist some differences on the ee obtained by chirality trabsfer.They ranged from 83% to 97%.