Angelw: synthesis of bifunctional allylic compounds with cyclopropene as allylic equivalent

Allylsilane and allyl alcohol derivatives are widely used as basic organic synthons If they are combined in the same allyl system to form a structural unit with two functional groups, the structure will have great potential in functional group transformation But at present, chemists have little research on this kind of structure Recently, Professor Luis A L ó PEZ and Professor rube é n Vicente of the University of Oviedo in Spain have designed a very clever and challenging synthesis strategy (scheme 1a) for this kind of silane and hydroxyl bifunctional allylic compounds It is not easy to select suitable carbene precursor to insert Si-H bond of simple silane The challenge lies in the regioselective rearrangement of cyclopropene is required for the formation of carbene intermediate This intermolecular reaction may lead to many side reactions, such as the insertion of O-H bond It is found that the Si-H bond can be inserted by using rhodium and cyclopropene to form metal carbene intermediate, so as to synthesize allylic compounds with silane and hydroxyl bifunctional functions The related research results were published on angelw Chem Int ed (DOI: 10.1002 / anie 201806961) (source: angelw Chem Int ed.) firstly, the author screened the reaction conditions with cyclopropene methanol derivatives 1a and triethylsilane 2A as substrates (scheme 1b) The experimental results show that zinc bromide, copper or silver as metal catalysts can not achieve ideal results When [Rh (octanoate) 2] 2 is used as catalyst, the reaction efficiency is improved obviously Only 1.2 equivalent silane is needed to obtain the target product 3a in 93% yield Then, the substrate applicability of the reaction was studied The results show that the reaction has a wide range of substrate applications Cyclopropene methanol derived from aldehydes or ketones is a suitable reaction substrate (scheme 2A1 and A2) When there are electron rich or electron deficient substituents such as benzene ring, heterocycle and ferrocene on cyclopropene methanol, the reaction can take place, and the corresponding target product can be obtained in good yield The substrate containing phenolic hydroxyl or alkenyl group can also be tolerated, showing the excellent chemical selectivity of the reaction Aliphatic alkyl or alkenyl substituted cyclopropene methanol can also participate in the reaction In addition, a variety of silanes, including triethylsilane, can also participate in the reaction Even triphenylsilane with large steric hindrance can obtain the corresponding product 3aG (scheme 2b) in 78% yield (source: angelw Chem Int ed.) through further study, the author found that the reaction is also suitable for intramolecular conversion and used to synthesize epoxy silane (scheme 3a) In addition, besides the synthesis of silane and hydroxyl bifunctional allylic compounds, the silane and amino bifunctional allylic compounds can also be prepared under this reaction condition (scheme 3b) (source: angelw Chem Int ed.) later, the author studied the mechanism of the reaction (scheme 4a) The reaction of compounds 9 and 2A shows that the selectivity of the reaction is mainly dominated by the substituents on cyclopropene rather than the oxygen atom Furthermore, the kinetic isotope effect (KIE) experiments of [D] - 2A, 2a and 1a in the deuterium belt were carried out The results show that the value of KH / KD is 2.3, which indicates that the fracture of Si-H bond is related to the rate determining step of the reaction According to this, the possible mechanism of the reaction (scheme4b) is proposed: firstly, 1-rh complex is obtained by the coordination of Cyclopropanol with rhodium catalyst, then it is converted into cyclopropyl cation intermediate I, then Rh (II) - carbene intermediate II is obtained, finally the target compound is obtained by Si-H bond insertion reaction (source: angelw Chem Int ed.) finally, the author proved the application value of the reaction in the synthesis through the transformation of representative functional groups such as oxidation, fluorination and Simmons Smith reaction (scheme 5) (source: angelw Chem Int ed.) conclusion: Professor Luis A L ó PEZ and Professor rub é n Vicente of Oviedo University in Spain have developed a method to prepare silane and hydroxydifunctional allylic compounds by using silane and cyclopropene The reaction can be carried out at room temperature with Rh (II) as catalyst The conditions are mild and the substrate range is very wide It can also be used for the synthesis of silane and amino bifunctional allylic compounds.