Exploiting Alkylquinone Tautomerization: Amine Benzylation

A general protocol for the synthesis of benzylic amines via side-chain amination of alkylquinones is reported. The reactions are initiated by the tautomerization of an alkylquinone to the corresponding quinone methide, which is subsequently trapped in situ by an amine nucleophile. This process is promoted by tertiary amines in protic solvents under mild conditions and is compatible with many functional groups. 1,2- and 1,4-benzoquinones, as well as naphthoquinones, participate in this reaction using a wide range of primary and secondary amines/anilines. The synthetic utility of this transformation is also explored

Direct β‑Alkylation of Aldehydes via Photoredox Organocatalysis

Direct β-alkylation of saturated aldehydes has been accomplished by synergistically combining photo­redox catalysis and organo­catalysis. Photon-induced enamine oxidation provides an activated β-enaminyl radical intermediate, which readily combines with a wide range of Michael acceptors to produce β-alkyl aldehydes in a highly efficient manner. Furthermore, this redox-neutral, atom-economical C–H functionalization protocol can be achieved both inter- and intramolecularly. Mechanistic studies by various spectro­scopic methods suggest that a reductive quenching pathway is operable

Exploiting Alkylquinone Tautomerization for the Total Synthesis of Calothrixin A and B

The pentacyclic alkaloid calothrixin B (<b>1</b>) has been synthesized in 5 steps from murrayaquinone A (<b>9</b>). The key step involved the union of boryl aniline <b>31</b> with brominated murrayaquinone A (<b>26</b>). In this transformation, alkylquinone <b>26</b> undergoes tautomerization to a quinone methide, which is intercepted by boryl aniline <b>31</b> to forge a new C–N bond. An intramolecular Suzuki coupling, followed by dehydrogenative aromatization, completed the synthesis of calothrixin B. Subsequent N-oxidation of calothrixin B delivered calothrixin A. The successful synthesis of these alkaloids and the challenges that led to the development of the final synthesis plan are reported herein

Exploiting Alkylquinone Tautomerization for the Total Synthesis of Calothrixin A and B

The pentacyclic alkaloid calothrixin B (<b>1</b>) has been synthesized in 5 steps from murrayaquinone A (<b>9</b>). The key step involved the union of boryl aniline <b>31</b> with brominated murrayaquinone A (<b>26</b>). In this transformation, alkylquinone <b>26</b> undergoes tautomerization to a quinone methide, which is intercepted by boryl aniline <b>31</b> to forge a new C–N bond. An intramolecular Suzuki coupling, followed by dehydrogenative aromatization, completed the synthesis of calothrixin B. Subsequent N-oxidation of calothrixin B delivered calothrixin A. The successful synthesis of these alkaloids and the challenges that led to the development of the final synthesis plan are reported herein