An elusive thermal [2 + 2] cycloaddition driven by visible light photocatalysis: tapping into strain to access C2-symmetric tricyclic ringsElectronic supplementary information (ESI) available: Experimental procedures, characterization, and spectral data. CCDC 1581327, 1814020 and 1840823. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c8ob01273c
A mild and operationally simple methodology is reported for the synthesis of cyclobutane rings imbedded within a C 2-symmetric tricyclic framework. The method uses visible light and an iridium-based photocatalyst to drive the oft-stated "forbidden" thermal [2 + 2] cycloaddition of cyclohep...
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Main Authors | , , |
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Format | Journal Article |
Published |
13.02.2019
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Online Access | Get full text |
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Summary: | A mild and operationally simple methodology is reported for the synthesis of cyclobutane rings imbedded within a
C
2-symmetric tricyclic framework. The method uses visible light and an iridium-based photocatalyst to drive the oft-stated "forbidden" thermal [2 + 2] cycloaddition of cycloheptenes and analogs. Importantly, it generates cyclobutane with four new stereocenters with excellent stereoselectivity, and perfect regioselectivity. The reaction is propelled forward when the photocatalyst absorbs a visible light photon, which transfers this energy to the cycloheptene. Key to success is, upon excitation to the triplet
via
sensitization from the photocatalyst, the double bond isomerizes to give the transient, highly strained,
trans
-cycloheptene. The
trans
-cycloheptene undergoes a strain relieving thermal, intermolecular [
π
2
s
+
π
2
a
] cycloaddition with another
cis
-cycloheptene. X-ray analysis reveals that the major product is the head-to-head,
C
2-symmetric all
trans
-cyclobutane. Additionally, a dramatic display structural complexity enhancement is observed with the use of chiral cycloheptenols possessing one stereocenter, which results in the formation of cyclobutanes with six contiguous stereocenters with good to excellent diastereocontrol, and can be used to isolate single stereoisomers of stereochemically complex cyclobutanes in good yield.
A mild and operationally simple methodology is reported for the synthesis of cyclobutane rings imbedded within a
C
2-symmetric tricyclic framework. |
---|---|
Bibliography: | For ESI and crystallographic data in CIF or other electronic format see DOI 1840823 1581327 10.1039/c8ob01273c and , Electronic supplementary information (ESI) available: Experimental procedures, characterization, and spectral data. CCDC 1814020 |
ISSN: | 1477-0520 1477-0539 |
DOI: | 10.1039/c8ob01273c |