Search

Iridium-catalyzed reductive nucleophilic addition to N-methoxyamides is reported. The reaction took place in high yields in the presence of a variety of sensitive functional groups such as esters and nitro groups. Mechanistic studies revealed that the reaction of N-methoxyamides proceeded without equilibrium to an enamine intermediate in contrast to that with tert-amides.

As the complexity of targeted molecules increases in modern organic synthesis, chemoselectivity is recognized as an important factor in the development of new methodologies. Chemoselective nucleophilic addition to amide carbonyl centers is a challenge because classical methods require harsh reaction conditions to overcome the poor electrophilicity of the amide carbonyl group. We have successfully developed a reductive nucleophilic addition of mild nucleophiles to tertiary amides, secondary amides, and N-methoxyamides that uses the Schwartz reagent [Cp2 ZrHCl]. The reaction took place in a highly chemoselective fashion in the presence of a variety of sensitive functional groups, such as methyl esters, which conventionally require protection prior to nucleophilic addition. The reaction will be applicable to the concise synthesis of complex natural alkaloids from readily available amide groups., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A chemoselective approach for the total synthesis of (±)-gephyrotoxin has been developed. The key to success was the utilization of N-methoxyamides, which enabled the direct coupling of the amide with an aldehyde and selective reductive nucleophilic addition to the amide in the presence of a variety of sensitive and electrophilic functional groups, such as a methyl ester. This chemoselective approach minimized the use of protecting-group manipulations and redox reactions, which resulted in the most concise and efficient total synthesis of (±)-gephyrotoxin described to date., (Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

While the synthesis of amide bonds is now one of the most reliable organic reactions, functionalization of amide carbonyl groups has been a long-standing issue due to their high stability. As an ongoing program aimed at practical transformation of amides, we developed a direct nucleophilic addition to N-alkoxyamides to access multisubstituted amines. The reaction enabled installation of two different functional groups to amide carbonyl groups in one pot. The N-alkoxy group played important roles in this reaction. First, it removed the requirement for an extra preactivation step prior to nucleophilic addition to activate inert amide carbonyl groups. Second, the N-alkoxy group formed a five-membered chelated complex after the first nucleophilic addition, resulting in suppression of an extra addition of the first nucleophile. While diisobutylaluminum hydride (DIBAL-H) and organolithium reagents were suitable as the first nucleophile, allylation, cyanation, and vinylation were possible in the second addition including inter- and intramolecular reactions. The yields were generally high, even in the synthesis of sterically hindered α-trisubstituted amines. The reaction exhibited wide substrate scope, including acyclic amides, five- and six-membered lactams, and macrolactams., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Direct allylation of inert amide carbonyls utilizing the Schwartz reagent afforded either substituted tertiary or secondary amines. A preactivation step was successfully avoided, which is generally a requisite to increase the electrophilicity of amides. The reaction exhibited remarkable functional group tolerance and proceeded even in the presence of methyl esters and nitro groups., (© 2012 American Chemical Society)

The total synthesis of lobatamides A (1 a) and C (1 c) via a common bislactone intermediate is reported. The allylic aryl moiety including a trisubstituted Z‐olefin was constructed by hydroboration of a 1,1‐disubstituted allene and subsequent Migita‐Kosugi‐Stille coupling. Although the seco acid proved to be highly unstable even in the presence of weak bases, Zhao macrolactonization under acidic conditions via the α‐acyloxyenamide successfully provided the common bislactone intermediate. Hydrozirconation‐iodination of the terminal alkyne and subsequent copper‐mediated coupling with primary amides proceeded successfully in the presence of the sensitive bislactone framework. The developed synthetic route enables the late‐stage installation of enamide side chains, which are crucial structures for V‐ATPase inhibition. [ABSTRACT FROM AUTHOR]

A reductive (3+2) annulation of lactams through iridium‐catalyzed hydrosilylation and photoredox coupling with α‐bromoacetic acid was developed. The iridium‐catalyzed hydrosilylation of the lactam carbonyl group and subsequent elimination provide a transient cyclic enamine, which undergoes iridium‐catalyzed photoredox coupling with α‐bromoacetic acid in a one‐pot process. The developed conditions show high functional‐group tolerance and provide cyclic N,O‐acetals containing a quaternary carbon center. The resulting N,O‐acetals undergo a variety of acid‐mediated nucleophilic addition reactions via iminium ions to give substituted cyclic amines. The developed sequence including reductive (3+2) annulation and acid‐mediated nucleophilic addition was successfully applied to the four‐step total synthesis of (±)‐eburnamonine. [ABSTRACT FROM AUTHOR]

Totally substituted butenolide including two tetrasubstituted olefins is a distinct structural motif seen in Stemona alkaloids, but efficient methods for its synthesis are not well developed. As an ongoing program aimed at the collective total synthesis of the stemoamide group, we report a stereodivergent method to give either (E)- or (Z)-totally substituted butenolide from the same intermediate. While AgOTf--mediated elimination via an E1-type mechanism results in the formation of the kinetic (Z)-tetrasubstituted olefin, subsequent TfOH-mediated isomerization gives the thermodynamic (E)-tetrasubstituted olefin. The pyrrole ring is another important structure found in Stemona alkaloids. The direct oxidation of pyrrolidine rings with MnO2 and careful purification gives the pyrrole groups without isomerization of the stereocenter in the lactone group. These two methods enabled us to synthesize a series of stemoamide-type alkaloids including tricyclic, tetracyclic, and pentacyclic frameworks. The anti-inflammatory activities by inhibition of iNOS expression in macrophage cell line RAW264.7 indicate that the most potent anti-inflammatory compounds without cytotoxicity are protostemonines, which consist of pentacyclic frameworks including the totally substituted butenolide. [ABSTRACT FROM AUTHOR]

The asymmetric total synthesis of fasicularin by a chiral N -alkoxyamide strategy is reported. Incorporation of the chiral alkoxy group onto an amide nitrogen changes the original reactivity of the amide, enabling two key transformations: aza-spirocyclization and the reductive Strecker reaction. DFT calculations indicate that pyramidalization of the N -alkoxyamide nitrogen is crucial to produce a cyclic hemiaminal in equilibrium, which undergoes aza-spirocyclization. The chiral alkoxy group is also used as a stereocontrol element to establish two consecutive stereocenters. The iridium-catalyzed reductive Strecker reaction of the N -alkoxylactam provides the aminonitrile with high diastereoselectivity. [ABSTRACT FROM AUTHOR]

A copper‐catalyzed electrophilic amidation of aryltrifluoroborates with use of N‐methoxyamides is reported. The reaction shows high functional group compatibility derived from two distinct features: 1) the high stability of the N‐methoxyamides and 2) the nonbasic mild conditions in the presence of LiCl. The developed method can also be applied to the synthesis of enamides, which are widely distributed in natural products. Preliminary mechanistic studies suggest that the initial step is the transmetalation of the aryltrifluoroborate by the assistance of LiCl, and the resulting aryl copper intermediate provides the anilide through non‐SN2 oxidative addition to the N‐methoxyamide and subsequent reductive elimination. [ABSTRACT FROM AUTHOR]

An approach to cyclic nitrones from N‐hydroxylactam derivatives is documented. The nucleophilic addition of an organolithium reagent to an N‐OSEM [SEM=2‐(trimethylsilyl)ethoxymethyl] lactam forms a five‐membered chelated intermediate, which undergoes both elimination and deprotection to give a fully substituted nitrone in a one‐pot process. When combined with the N‐oxidation of easily available chiral lactams, this method becomes especially useful for the quick synthesis of chiral nitrones in enantio‐pure form, enabling the concise total synthesis of cylindricine C. Fully substituted cyclic nitrones are accessed from N‐hydroxylactam derivatives. The reaction proceeds through nucleophilic addition of an organolithium reagent and subsequent elimination in a one‐pot process. When combined with N‐oxidation of a chiral lactam, the method allows utilization of an easily available lactam as a chiral nitrone equivalent, enabling the enantioselective total synthesis of cylindricine C. [ABSTRACT FROM AUTHOR]

As the complexity of targeted molecules increases in modern organic synthesis, chemoselectivity is recognized as an important factor in the development of new methodologies. Chemoselective nucleophilic addition to amide carbonyl centers is a challenge because classical methods require harsh reaction conditions to overcome the poor electrophilicity of the amide carbonyl group. We have successfully developed a reductive nucleophilic addition of mild nucleophiles to tertiary amides, secondary amides, and N-methoxyamides that uses the Schwartz reagent [Cp2ZrHCl]. The reaction took place in a highly chemoselective fashion in the presence of a variety of sensitive functional groups, such as methyl esters, which conventionally require protection prior to nucleophilic addition. The reaction will be applicable to the concise synthesis of complex natural alkaloids from readily available amide groups. [ABSTRACT FROM AUTHOR]

The development of a two-step synthesis of multi-substituted N-methoxyamines from N-methoxyamides is reported. Utilization of the N-methoxy group as a reactivity control element was the key to success in this two-step synthesis. The first reaction involves a N-methoxyamide/aldehyde coupling reaction. Whereas ordinary amides cannot condense with aldehydes intermolecularly due to the poor nucleophilicity of the amide nitrogen, the N-methoxy group enhances the nucleophilicity of the nitrogen, enabling the direct coupling reaction. The second reaction in the two-step process was nucleophilic addition to the N-methoxyamides. Incorporation of the N-methoxy group into the amides increased the electrophilicity of the amide carbonyls and promoted the chelation effect. This nucleophilic addition enabled quick diversification of the products derived from the first step. The developed strategy was applicable to a variety of substrates, resulting in the elaboration of multi-substituted piperidines and acyclic amines, as well as a substructure of a complex natural alkaloid. [ABSTRACT FROM AUTHOR]

A chemoselective approach for the total synthesis of (±)-gephyrotoxin has been developed. The key to success was the utilization of N-methoxyamides, which enabled the direct coupling of the amide with an aldehyde and selective reductive nucleophilic addition to the amide in the presence of a variety of sensitive and electrophilic functional groups, such as a methyl ester. This chemoselective approach minimized the use of protecting-group manipulations and redox reactions, which resulted in the most concise and efficient total synthesis of (±)-gephyrotoxin described to date. [ABSTRACT FROM AUTHOR]

While the synthesis of amide bonds is now one of the most reliable organic reactions, functionalization of amide carbonyl groups has been a long-standing issue due to their high stability. As an ongoing program aimed at practical transformation of amides, we developed a direct nucleophilic addition to N-alkoxyamides to access multisubstituted amines. The reaction enabled installation of two different functional groups to amide carbonyl groups in one pot. The N-alkoxy group played important roles in this reaction. First, it removed the requirement for an extra preactivation step prior to nucleophilic addition to activate inert amide carbonyl groups. Second, the N-alkoxy group formed a five-membered chelated complex after the first nucleophilic addition, resulting in suppression of an extra addition of the first nucleophile. While diisobutylaluminum hydride (DIBAL-H) and organolithium reagents were suitable as the first nucleophile, allylation, cyanation, and vinylation were possible in the second addition including inter- and intramolecular reactions. The yields were generally high, even in the synthesis of sterically hindered α-trisubstituted amines. The reaction exhibited wide substrate scope, including acyclic amides, five- and six-membered lactams, and macrolactams. [ABSTRACT FROM AUTHOR]

Review: 9 refs. [ABSTRACT FROM AUTHOR]

In “old man flower”, a Japanese story, the kind old man sprinkled ashes and made dead trees blossom all over. Incorporation of a methoxy group to an amide group opens the door to new reactivities and allows beautiful chemical transformations to blossom in organic synthesis. For more details, see the Full paper by T. Sato, N. Chida et al. on page 8210 ff. We thank Miwako Yoritate and Takamasa Wada for their assistance with artwork. [ABSTRACT FROM AUTHOR]

The title transformation consists of (i) reduction of the amide carbonyl group, (ii) formation of an iminium ion with an acid, and (iii) C-C bond formation with a mild nucleophile. [ABSTRACT FROM AUTHOR]

Two novel types of Overman rearrangements from vicinal diols are developed by simply changing the reaction conditions. [ABSTRACT FROM AUTHOR]