Direct Access to Unnatural Cyclobutane α-Amino Acids through Visible Light Catalyzed [2+2]-Cycloaddition

Abstract

In this work, we report the first selective, photocatalyzed [2+2]-cycloaddition of dehydroamino acids with styrenetype olefins. This simple, mild, and scalable approach relies on the use of the triplet energy transfer catalyst [Ir(dFCF 3 ppy 2 )dtbpy]PF 6 under visible light irradiation and provides fast access to valueadded substituted strained cyclobutane α-amino acid derivatives.

Hydrogen‐Bonding Organocatalysis Enabled Photocatalytic Intramolecular [2+2]‐Cycloaddition Reaction

“…Inspired by the mentioned breakthroughs and following our program on synthetic photocatalytic methods, [17] we envisioned an intermolecular [2+2]‐cycloaddition triggered by HB‐activation of substrates bearing only one Lewis base binding site (Scheme 1c). Hence, we present the activation of enone‐ene derivatives by the combination of an iridium photocatalyst and a simple bidentate hydrogen bonding catalyst, allowing to extend the reaction media in which this process can be performed.…”

Recent Advances in Photoinduced Modification of Amino Acids, Peptides, and Proteins

“…[41] In this context, the Mancheño group first described a photocatalytic [2 + 2] cycloaddition of dehydroamino acids 54 with styrene-type olefins 55 (Scheme 20). [42] The protocol was based on the use of the triplet energy transfer catalyst [Ir(dFCF 3 ppy 2 )dtbpy]PF 6, (Ir [3]) which has a potent triplet sensitizer energy (E T ) of 61.8 kcal mol À 1 and enables energy transfer to the styrene derivative (60 kcal mol À 1 ). Thus, under visible light conditions, strained substituted cyclobutene α-amino acid derivatives were prepared in good yields, great 1,2-regioselectivity and diastereoselectivity of up to 20 : 1 d.r.…”

Advances in Organic and Inorganic Photoredox Catalysis

“…Here, Olga Garci ́a Manchenõ et al disclose intermolecular [2 + 2] photocycloaddition reactions between enamides and styrenes for the direct synthesis of unnatural 2-substituted cyclobutane α-amino acids. 21 The method employs [[Ir(dFCF 3 ppy 2 )dtbpy]PF 6 as a photoredox catalyst, and a variety of cyclobutanes were prepared in good yields. In addition, Christoforos Kokotos et al report the synthesis of cyclobutanes via [2 + 2] cycloaddition between N-aryl maleimides and styrenes, catalyzed by thioxanthone as an organic sensitizer.…”

“…Visible-light mediated [2 + 2] cycloaddition via energy transfer mechanism is a valuable method for the synthesis of highly strained cyclobutanes. Here, Olga García Mancheño et al disclose intermolecular [2 + 2] photocycloaddition reactions between enamides and styrenes for the direct synthesis of unnatural 2-substituted cyclobutane α-amino acids . The method employs [[Ir­(dFCF 3 ppy 2 )­dtbpy]­PF 6 as a photoredox catalyst, and a variety of cyclobutanes were prepared in good yields.…”