4144-59-6

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We present herein a novel strategy for the preparation of ketones from aldehydes and allylic boronic esters. This reaction involves the allylation of aldehydes with allylic boronic esters and the Rh-catalyzed chain-walking of homoallylic alcohols. The key to this successful development is the protodeboronation of alkenyl borylether intermediate via a tetravalent borate anion species in the presence of KHF2 and MeOH. This approach features mild reaction conditions, broad substrate scope, and excellent functional group tolerance. Mechanistic studies also supported that the tandem allylation and chain-walking process were involved.

The reaction of 2-substituted cycloalkanones with cerium(IV) sulfate tetrahydrate (CS) in alcohols and acetic acid gave the corresponding alkyl esters of oxo acids (80-96%) and oxo acids (78-96%), respectively, by oxidative cleavage of the C(R).C=O bond. In the case of 2-iodocycloalkanones in methanol, the dimethyl ester was obtained in good yield. A treatment of 5α-cholestan-3-one with CS in methanol produced 2-acetal 3-ester of 2,3-seco derivative in good yield. The effects of cerium(IV) and copper(II) salts are also discussed.

Thiols catalyse the radical-chain addition of primary aliphatic aldehydes R1CH2CHO to terminal alkenes H2C=CR2R3 to give ketonic adducts R1CH2C(O)CH2C(H)R2R3 in moderate to good yields.The reaction takes place under mild conditions (dioxane solvent, 60 deg C) and is initiated by di-tert-butyl hyponitrite (TBHN).Thiol catalysis is effective for hydroacylation of electron-rich, -neutral and -deficient alkenes, but is most efficient for addition to electron-rich double bonds.For example, the addition of butanal (2 equiv.) to isopropenyl acetate in the presence of TBHN (2x2.5 molpercent) and methyl thioglycolate (MeO2CCH2SH; 2x5 molpercent) gives the adduct in 80percent yield, whilst a similar reaction in the absence of thiol catalyst affords only an 8percent yield.Other enol acetates, silyl enol ethers, an enol phosphate and butyl vinyl ether react similarly.For comparison, the reaction of butanoyl phenyl selenide with isopropenyl acetate, in the presence of tributyltin hydride and azoisobutyronitrile initiator in benzene at 80 deg C, gives the adduct in only 7percent yield.Methyl thioglycolate is generally the most efficient catalyst for hydroacylation of electron-rich alkenes, whilst tert-dodecanethiol is more effective for addition of aldehydes to electron-deficient alkenes.Triorganosilanethiols also function as catalysts, as does the arenethiol 2,4,6-tris(trifluoromethyl)thiophenol.The role of the thiol is to act as a polarity-reversal catalyst that promotes the overall hydrogen-atom transfer from the aldehyde to the carbon-centred radical produced by addition of the acyl radical to the alkene.Intramolecular hydroacylation is also subject to thiol catalysis and the radical-chain cyclisation of citronellal to a mixture of menthone and isomenthone is effectively promoted in the presence of triphenylsilanethiol.