Two facile, metal-and additive-free protocols for radical dehalogenation, deoxygenation and cyclization reactions are reported. Irradiation by household fluorescent light bulbs or the presence of an air atmosphere is shown to initiate the desired reactions, thus providing highly practical reaction setups for radical-mediated reductions and cyclizations. Scheme 1 Overview of previous and present work. † Electronic supplementary information (ESI) available. See
A general methodology for the synthesis of trisubstituted, optically active thiophenes by an organocatalytic one-pot reaction cascade is presented. The target products are synthesized in good yields (up to 92%) and with excellent enantioselectivities (up to 98% ee). Importantly, based on practical and easily available starting materials, the presented methodology can be conducted under mild reaction conditions. To further elucidate the generality, the synthesis of optically active thienoindoles, as well as selenophenes, is also demonstrated.
Matching catalyst and substrate: Organocatalytic cycloaddition between dienamines and 1,4‐benzo‐ or 1,4‐naphthoquinones affords biologically interesting dihydronaphtho‐ and dihydroanthraquinone core structures. The enantioselectivity of this new reaction is ensured by a steric shielding catalyst and carefully selecting substrates that greatly favor the endo approach (see scheme) due to electrostatic interactions in the zwitterionic intermediate.
The radical reduction of a variety of substrates, e.g. halogenides (V) and (VII), is achieved using (Tms)3SiH as hydride source and air or light as radical initiator. The dehalogenation of substrates (IX) and (XI) is accompanied by a cyclization reaction leading to dihydrobenzofuran (X) and benzofuran (XII), respectively. -(JIANG, H.; BAK, J. R.; LOPEZ-DELGADO, F. J.; JOERGENSEN*, K. A.; Green Chem. 15 (2013) 12, 3355-3359, http://dx.doi.org/10.1039/c3gc41520a ; Cent. Catal., Aarhus Univ., DK-8000 Aarhus, Den.; Eng.) -R. Staver 15-036
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