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Di Sabato A, D’Acunzo F, Filippini D, Vetica F, Brasiello A, Corinti D, Bodo E, Michenzi C, Panzetta E, Gentili P. Unusually Chemoselective Photocyclization of 2-(Hydroxyimino)aldehydes to Cyclobutanol Oximes: Synthetic, Stereochemical, and Mechanistic Aspects. J Org Chem 2022; 87:13803-13818. [PMID: 36198009 PMCID: PMC9639046 DOI: 10.1021/acs.joc.2c01503] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Photocyclization of carbonyl compounds (known as the Norrish-Yang reaction) to yield cyclobutanols is, in general, accompanied by fragmentation reactions. The latter are predominant in the case of aldehydes so that secondary cyclobutanols are not considered accessible via the straightforward Norrish-Yang reaction. A noteworthy exception has been reported in our laboratory, where cyclobutanols bearing a secondary alcohol function were observed upon UV light irradiation of 2-(hydroxyimino)aldehydes (HIAs). This reaction is here investigated in detail by combining synthesis, spectroscopic data, molecular dynamics, and DFT calculations. The synthetic methodology is generally applicable to a series of HIAs, affording the corresponding cyclobutanol oximes (CBOs) chemoselectively (i.e., without sizable fragmentation side-reactions), diastereoselectively (up to >99:1), and in good to excellent yields (up to 95%). CBO oxime ether derivatives can be purified and diastereomers isolated by standard column chromatography. The mechanistic and stereochemical picture of this photocyclization reaction, as well as of the postcyclization E/Z isomerization of the oxime double bond is completed.
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Affiliation(s)
- Antonio Di Sabato
- Department
of Chemistry, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy,Institute
of Biological Systems (ISB), Sezione Meccanismi di Reazione, Italian
National Research Council (CNR), c/o Department of Chemistry, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy
| | - Francesca D’Acunzo
- Institute
of Biological Systems (ISB), Sezione Meccanismi di Reazione, Italian
National Research Council (CNR), c/o Department of Chemistry, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy
| | - Dario Filippini
- Department
of Chemistry, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy
| | - Fabrizio Vetica
- Department
of Chemistry, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy,
| | - Antonio Brasiello
- Department
of Chemical Engineering Materials Environment, Sapienza University of Rome, via Eudossiana 18, 00184 Rome, Italy
| | - Davide Corinti
- Department
of Chemistry and Technology of Drugs, Sapienza
University of Rome, Piazzale
Aldo Moro 5, 00185 Rome, Italy
| | - Enrico Bodo
- Department
of Chemistry, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy
| | - Cinzia Michenzi
- Department
of Chemistry, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy
| | - Edoardo Panzetta
- Department
of Chemistry, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy
| | - Patrizia Gentili
- Department
of Chemistry, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy,Institute
of Biological Systems (ISB), Sezione Meccanismi di Reazione, Italian
National Research Council (CNR), c/o Department of Chemistry, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Rome, Italy,
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Braak FT, Elferink H, Houthuijs KJ, Oomens J, Martens J, Boltje TJ. Characterization of Elusive Reaction Intermediates Using Infrared Ion Spectroscopy: Application to the Experimental Characterization of Glycosyl Cations. Acc Chem Res 2022; 55:1669-1679. [PMID: 35616920 PMCID: PMC9219114 DOI: 10.1021/acs.accounts.2c00040] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
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A detailed
understanding of the reaction mechanism(s) leading to
stereoselective product formation is crucial to understanding and
predicting product formation and driving the development of new synthetic
methodology. One way to improve our understanding of reaction mechanisms
is to characterize the reaction intermediates involved in product
formation. Because these intermediates are reactive, they are often
unstable and therefore difficult to characterize using experimental
techniques. For example, glycosylation reactions are critical steps
in the chemical synthesis of oligosaccharides and need to be stereoselective
to provide the desired α- or β-diastereomer. It remains
challenging to predict and control the stereochemical outcome of glycosylation
reactions, and their reaction mechanisms remain a hotly debated topic.
In most cases, glycosylation reactions take place via reaction mechanisms
in the continuum between SN1- and SN2-like pathways.
SN2-like pathways proceeding via the displacement of a
contact ion pair are relatively well understood because the reaction
intermediates involved can be characterized by low-temperature NMR
spectroscopy. In contrast, the SN1-like pathways proceeding
via the solvent-separated ion pair, also known as the glycosyl cation,
are poorly understood. SN1-like pathways are more challenging
to investigate because the glycosyl cation intermediates involved
are highly reactive. The highly reactive nature of glycosyl cations
complicates their characterization because they have a short lifetime
and rapidly equilibrate with the corresponding contact ion pair. To
overcome this hurdle and enable the study of glycosyl cation stability
and structure, they can be generated in a mass spectrometer in the
absence of a solvent and counterion in the gas phase. The ease of
formation, stability, and fragmentation of glycosyl cations have been
studied using mass spectrometry (MS). However, MS alone provides little
information about the structure of glycosyl cations. By combining
mass spectrometry (MS) with infrared ion spectroscopy (IRIS), the
determination of the gas-phase structures of glycosyl cations has
been achieved. IRIS enables the recording of gas-phase infrared spectra
of glycosyl cations, which can be assigned by matching to reference
spectra predicted from quantum chemically calculated vibrational spectra.
Here, we review the experimental setups that enable IRIS of glycosyl
cations and discuss the various glycosyl cations that have been characterized
to date. The structure of glycosyl cations depends on the relative
configuration and structure of the monosaccharide substituents, which
can influence the structure through both steric and electronic effects.
The scope and relevance of gas-phase glycosyl cation structures in
relation to their corresponding condensed-phase structures are also
discussed. We expect that the workflow reviewed here to study glycosyl
cation structure and reactivity can be extended to many other reaction
types involving difficult-to-characterize ionic intermediates.
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Affiliation(s)
- Floor ter Braak
- Radboud University, Institute for Molecules and Materials, Synthetic Organic Chemistry, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
| | - Hidde Elferink
- Radboud University, Institute for Molecules and Materials, Synthetic Organic Chemistry, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
| | - Kas J. Houthuijs
- Radboud University, FELIX Laboratory, Institute of Molecules and Materials, Toernooiveld 7, 6525 ED Nijmegen, The Netherlands
| | - Jos Oomens
- Radboud University, FELIX Laboratory, Institute of Molecules and Materials, Toernooiveld 7, 6525 ED Nijmegen, The Netherlands
| | - Jonathan Martens
- Radboud University, FELIX Laboratory, Institute of Molecules and Materials, Toernooiveld 7, 6525 ED Nijmegen, The Netherlands
| | - Thomas J. Boltje
- Radboud University, Institute for Molecules and Materials, Synthetic Organic Chemistry, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
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