TY  - JOUR
A1  - Fudickar, Werner
A1  - Metz, Melanie
A1  - Mai-Linde, Yasemin
A1  - Krüger, Tobias
A1  - Kelling, Alexandra
A1  - Sperlich, Eric
A1  - Linker, Torsten
T1  - Influence of functional groups on the ene reaction of singlet oxygen with 1,4-cyclohexadienes
JF  - Photochemistry and photobiology : the official journal of the American Society for Photobiology
N2  - The photooxygenation of 1,4-cyclohexadienes has been studied with a special focus on regio- and stereoselectivities. In all examples, only the methyl-substituted double bond undergoes an ene reaction with singlet oxygen, to afford hydroperoxides in moderate to good yields. We explain the high regioselectivities by a "large-group effect" of the adjacent quaternary stereocenter. Nitriles decrease the reactivity of singlet oxygen, presumably by quenching, but can stabilize proposed per-epoxide intermediates by polar interactions resulting in different stereoselectivities. Spiro lactams and lactones show an interesting effect on regio- and stereoselectivities of the ene reactions. Thus, singlet oxygen attacks the double bond preferentially anti to the carbonyl group, affording only one regioisomeric hydroperoxide. If the reaction occurs from the opposite face, the other regioisomer is exclusively formed by severe electrostatic repulsion in a perepoxide intermediate. We explain this unusual behavior by the fixed geometry of spiro compounds and call it a "spiro effect" in singlet oxygen ene reactions.
Y1  - 2021
U6  - https://doi.org/10.1111/php.13422
SN  - 0031-8655
SN  - 1751-1097
VL  - 97
IS  - 6
SP  - 1289
EP  - 1297
PB  - Wiley
CY  - Malden, Mass.
ER  - 
TY  - JOUR
A1  - Krüger, Tobias
A1  - Bramborg, Andrea
A1  - Kelling, Alexandra
A1  - Sperlich, Eric
A1  - Linker, Torsten
T1  - Birch Reduction of Arenes as an Easy Entry to γ-Spirolactones
JF  - European journal of organic chemistry
N2  - A convenient method for the synthesis of γ-spirolactones in only 2–3 steps is described. Birch reduction of inexpensive and commercially available aromatic carboxylic acids in the presence of ethylene oxide affords hydroxy acids, which undergo direct lactonization during work-up. Suitable precursors are methyl-substituted benzoic acids, naphthoic, and dicarboxylic acids. Subsequent hydrogenation proceeds smoothly with Pd/C as catalyst and saturated γ-spirolactones are isolated in excellent yields and stereoselectivities. Thus, up to 3 new stereogenic centers can be constructed as sole diastereomers from achiral benzoic acids. Furthermore, it is possible to control the degree of saturation with Raney nickel or Wilkinson's catalyst to obtain products with 1 double bond. Overall, more than 30 new γ-spirolactones have been synthesized in analytically pure form.
KW  - Arenes
KW  - Birch reduction
KW  - Hydrogenation
KW  - Lactones
KW  - Synthetic methods
Y1  - 2021
U6  - https://doi.org/10.1002/ejoc.202101018
SN  - 1434-193X
SN  - 1099-0690
VL  - 2021
IS  - 46
SP  - 6383
EP  - 6391
PB  - Wiley-VCH
CY  - Weinheim
ER  -