Organocatalytic Enantio Selective Allylic Silicon Etherification Of Morita-Baylis-Hillman Carbonates And Silanols

The asymmetric nucleophilic substitution reactions of allylic substrates and various nucleophiles(such as C,N,O,P,S,B)are powerful methods to construct carbon-carbon and carbon-heteroatom bonds,which play an important role in the field of organic synthesis.Allylsilicon compounds have the important application in total synthesis of sesquiterpenes,pharmaceuticals and complex cyclic compounds.The reaction of asymmetric allylic etherification has attracted chemists' extensive attention both in transition metal-catalysts and organocatalysts.By contrast,silicon nucleophiles such as silanes and silanols have been less studied in the asymmetric allylic substitution reactions.Three works have been reported in asymmetric allylic silicon etherification which Ph3 SiOH as the nucleophile and transition metal as the catalyst.Due to the transition metal catalysts with its drawbacks of expensive price and hard reaction condition,we chose the chiral cinchona alkaloids as the catalysts with its metric of mild reaction condition,strong stability and friendly to environment.We research in asymmetric allylic silicon etherification of silanols and MBH carbonates which are harder to control the regioselectivities.Initially,Ph3 SiH was used as the nucleophile to react with MBH carbonates.Structure of the product was confirmed by X-ray diffraction.Surprisedly,we found that Ph3SiO-substituted MBH carbonate was conformed.We performed a series of control experiments and found that Ph3 SiH could be transformed into Ph3 SiOH under the reaction condition.Subsequently,we used Ph3 SiOH as the nucleophile directly,and made some detailed research in asymmetric allylic substitution reaction between MBH carbonates and silanols from catalysts,base,ratio of the substrates,temperature and solvent.When(DHQD)2PYR(10 mol %)was used as the catalyst,iPr2 EtN was used as the base in MTBE at 90 oC for 12 h,the product was obtained in 91% yield,high regioselectivity(>20:1)and 90% ee value.With the optimal condition,a series of aromatic,heterocyclic or aliphatic Morita-Baylis-Hillman carbonates(25 examples)worked well with triphenylsilanol,affording the corresponding products in moderate to good yields(up to 98%),high regioselectivities(>20:1)and good enantioselectivities(up to 92%).When dimethylphenylsilanol was used as the nucleophile,the product was obtained in 60% yield and 87% ee value.Later,some suitable derivatives of the product were synthesized.In this work,not only the chiral alcohol compounds could be afforded that Ph3 SiOH was used as the water surrogate but the chiral silicon contained compounds could be obtained.We extented the applicatipon of organocatalysts in asymmetric allylic silicon etherification reaction.All the new compounds in the paper were confirmed by 1H NMR,13 C NMR,HRMS.Absolute configuration of the product and some product's structure were confirmed by X-ray diffraction.