Synthesis of arylacetaldehyde from arylboric acid and 1,3-dioxolapentene-2-one catalyzed by angelw: IR

Arylacetaldehyde has become the focus of chemical researchers because of its great potential for synthesis The synthesis of arylacetaldehyde can be divided into two main methods: alcohol, selective oxidation of aryl ethylene, reduction of carboxylic acid, hydrolysis of arylethyne and other functional group conversion (type 1, scheme 1a) and C-C bond formation (type 2, scheme 1b) However, the synthesis of aryl acetaldehyde by type2 method has some problems, such as complicated steps and poor selectivity Therefore, the team of Tamio Hayashi from Nanyang University of technology has developed a new strategy (scheme 1c) for the direct generation of arylacetaldehyde from arylboric acid and 1,3-dioxocyclopentadiene-2-one catalyzed by IR This strategy provides a new way for the synthesis of arylacetaldehyde Relevant research results were published in angelw Chem Int ed (DOI: 10.1002 / anie 201906148) (picture source: angel Chem Int ed.) firstly, the author used 1,3-dioxocyclopentadiene-2-one-1 and 3,4 - (methylenedioxy) phenylboronic acid-2a as template substrate Through the screening of catalyst, solvent and additives, the optimal conditions were determined as (Table 1): 5.0 mol% [irome (COD)] 2 and 5.5 mol% DPPP ome ligand as catalyst, 5.5 mol% B 2 (OH) 4 is the additive, clch2cl2 CL / H2O (10:1) is the solvent, and the corresponding product 3A can be obtained in 75% yield at 90 ° C for 1 h (picture source: angelw Chem Int ed.) then, under the optimal reaction conditions, the author investigated the substrate range of the reaction (Table 2) All kinds of para - or meta substituted arylboric acid can adapt to the reaction conditions and get the corresponding products in good yield The 1-naphthylarboxylic acid with higher steric hindrance also has good tolerance, and the corresponding product can be obtained in good yield If 3,4 - (methylenedioxy) phenylboric acid is replaced by unsubstituted phenylboric acid, the corresponding product can only be obtained in medium yield By optimizing the reaction conditions, the yield of the reaction can also be increased from 57% to 66% (picture source: angelw Chem Int ed.) the author speculates the possible mechanism (scheme 2): first, the catalyst IR and the arylboric acid generate the [IR] - AR intermediate a through the metal transfer process Then, a will react with 1,3-dioxapharapentene-2-one-1 to form alkyl IR intermediate B Then, B undergoes β - oxygen elimination reaction to form intermediate C At last, C was hydrolyzed, decarboxylated and ketone enol isomerized to produce arylacetaldehyde 3 and regenerate [IR] - Oh at the same time (picture source: angelw Chem Int ed.) in order to further understand the role of additive B 2 (OH) 4 in this reaction, the author conducted a series of control experiments (scheme 3) Two same reactions, one with B 2 (OH) 4 and the other without B 2 (OH) 4, were carried out at 70 ℃ for 15 minutes It was found that the reaction with B 2 (OH) 4 can obtain the product in 62% yield, while the reaction without B 2 (OH) 4 can only obtain the product in 8% yield (scheme 3a) If 1,3-dioxolapentene-2-one-1 is not added in the reaction, in the same way, B 2 (OH) 4 is added in one of the reactions and B 2 (OH) 4 is not added in the other, the author found that arylphenylboric acid will hydrolyze to B 2 (OH) 4 and aroh, but the hydrolysis speed of the reaction without B 2 (OH) 4 is much slower than that of the reaction with B 2 (OH) 4 These results show that B 2 (OH) 4 can promote the conversion of ARB (OH) 2 to Ar-H, that is, B 2 (OH) 4 plays an important role in metal transfer and hydrolysis Considering the high yield of the reaction products, the author speculates that B 2 (OH) 4 is more likely to promote the metal transfer process (scheme3b) The recovery of 1 is the same with or without B 2 (OH) 4, which shows that B 2 (OH) 4 is independent of the reaction process in which 1 participates (scheme 3C) (photo source: angelw Chem Int ed.) Summary: team Tamio Hayashi of Nanyang University of technology has developed a new IR catalytic strategy for the direct generation of arylacetaldehyde from arylboric acid and 1,3-dioxolapentene-2-one This strategy provides a new way for the synthesis of arylacetaldehyde.