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. 2019 Dec 19;58(52):18918-18922.
doi: 10.1002/anie.201912132. Epub 2019 Nov 7.

Accessing 1,2-Substituted Cyclobutanes through 1,2-Azaborine Photoisomerization

Zachary X Giustra  1 , Xinyu Yang  1 , Min Chen  1 , Holger F Bettinger  2 , Shih-Yuan Liu  1
Affiliations

Accessing 1,2-Substituted Cyclobutanes through 1,2-Azaborine Photoisomerization

Zachary X Giustra et al. Angew Chem Int Ed Engl. .

Abstract

We provide a seminal example of the utility of the 1,2-azaborine motif as a 4C+1N+1B synthon in organic synthesis. Specifically, conditions for the practically scalable photoisomerization of 1,2-azaborine in a flow reactor are reported that furnish aminoborylated cyclobutane derivatives. The C-B bonds could also be functionalized to furnish a diverse set of highly substituted cyclobutanes.

Keywords: boron-nitrogen heterocycles; flow chemistry; photochemistry; small ring systems; valence isomerization.

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Conflict of interest statement

Conflict of interest

The authors declare no conflict of interest.

Figures

Scheme 1.
Scheme 1.
Developing the 1,2-azaborine motif as a 4C+1N+1B synthon in organic synthesis.
Scheme 2.
Scheme 2.
Examples of heterobicyclic precursors to isolated all-carbon four-membered rings (top) and proposed general sequence leading from 1,2-azaborine photoisomer 1 to 1,2-disubstituted cyclobutanes (bottom).
Scheme 3.
Scheme 3.
Flow photoisomerization of 1,2-azaborine 2. OtAm = tert-amyloxy.
Scheme 4.
Scheme 4.
Sequential isomerization/hydrogenation of 2 to azaborabicyclohexane 4 and subsequent ring opening to form aminoborylated cyclobutane 5.
Scheme 5.
Scheme 5.
Diastereoselective synthesis of hindered aminoborylated cyclobutanes. Isolated yields reported as the average of two runs.
Scheme 6.
Scheme 6.
Diastereoselective synthesis of hindered aminoborylated cyclobutanes. Isolated yields reported as the average of two runs.
Scheme 7.
Scheme 7.
Substrate scope of dual iridium photoredox/nickel-catalyzed cross-coupling of 7. Isolated yields reported as the average of two runs at 0.35 mmol scale. Values in parentheses are the trans:cis diastereomeric ratios of isolated material. [a] Using aryl iodide. [b] Isolated yield of trans diastereomer only. [c] From crude mixture 1H NMR analysis.
Scheme 8.
Scheme 8.
Additional C-B bond functionalizations.
See this image and copyright information in PMC

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