Aerobic Hydroxylation of N-Borylenamine: Triethylborane-Mediated Hydroxyalkylation of α,β-Unsaturated Oxime Ether

Abstract

Intermolecular hydroxyalkylation of alpha,beta-unsaturated imines involving Et3B-mediated regioselective alkyl radical addition and subsequent hydroxylation with molecular oxygen has been developed, in which N-borylenamine generated by trapping of the enaminyl radical with Et3B was a key intermediate in the proposed aerobic hydroxylation mechanism.

Free‐Radical Multicomponent Processes

“…This reaction was applied to cyclic as well as acyclic enoximes and hydrazones. Carbohydroxylation of enoximes such as 64 was developed based on the same strategy, giving rise to the corresponding oxime 65 in moderate yield and diastereoselectivity (2) [49]. Finally, based on the same approach, a domino reaction involving the conjugate addition of a thiyl radical onto a vinylcyclopropyloxime ether 66, in the presence of Et 3 B and oxygen, led to a boryl enamine of type 63, which was trapped by an aldehyde 67, affording the aldoltype product 68 in high yield and good diastereocontrol (3) [50].…”

Radical Addition of Arylboronic Acids to Various Olefins under Oxidative Conditions

“…Interestingly, we found that reaction of phenylboronic acid and methyl acrylate with Mn(OAc) 3 in the presence of dioxygen (balloon, 1 atm) did not provide the targeted tetrahydronaphthalene derivative but delivered product 2a as a result of a radical hydroxyarylation (Scheme , Table , entry 1) . Radical hydroxyalkylations are well established; however, the corresponding arylhydroxylation process is not well investigated to date . This is not unexpected since, due to the high reactivity of aryl radicals, intermolecular aryl radical additions are generally very difficult to achieve .…”

Radical Addition-Initiated Domino Reactions of Conjugated Oxime Ethers

“…Good diastereoselectivity was observed with substrate 9 bearing Oppolzer's camphorsultam, which gave the chiral β-hydroxy sulfide 14 in 70% yield [30][31][32][33][34] (Table 1, entry 1). The acyclic ketoxime ether 10 also reacted smoothly to afford the desired product with high stereoselectivity ( oselective construction of carbon-sulfur and carbon-oxygen bonds in a single operation, representing a highly efficient approach to the synthesis of β-hydroxy sulfides.…”

“…The acyclic ketoxime ether 10 also reacted smoothly to afford the desired product with high stereoselectivity ( oselective construction of carbon-sulfur and carbon-oxygen bonds in a single operation, representing a highly efficient approach to the synthesis of β-hydroxy sulfides. 35) Free radical-mediated hydroxyalkylation reactions involving both carbon-carbon bond formation and oxygenation processes represent an attractive approach for the preparation of complex molecules. [36][37][38][39][40][41][42][43][44][45] With this in mind, we investigated the triethylborane-induced hydroxyalkylation reaction of conjugated imines in the context of our previous study on hydroxysulfenylation.…”