Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

• et al. developed an iridium-based bifunctional hydrogen bonding photocatalyst 205. To demonstrate the effectiveness of this photocatalyst system, they tested the intramolecular photocycloaddition of quinolones 206 (Scheme 32a) [90]. The proposed mechanism again proceeds via a triplet sensitisation of

• enantioselectivity via triplet state intermediate 200, rather than proceeding via an enantioselective rearrangement. Bifunctional hydrogen bonding photocatalysts have been developed by other groups as well. Sivaguru developed an atropisomeric thiourea-based catalyst 201 and used it for the intramolecular

• photocycloaddition of coumarins 202 (Scheme 31) [89]. The proposed mechanism for this reaction is similar to that proposed by Bach and Krische, proceeding via a key hydrogen bonding complex 203. Interestingly, this catalyst allowed for reactivity with lactones, whereas Bach’s catalysts are limited to lactams. Yoon

Recent synthesis of thietanes

• Jiaxi Xu

Beilstein J. Org. Chem. 2020, 16, 1357–1410, doi:10.3762/bjoc.16.116

• into pyridoisoindolones 337 [94] (Scheme 65). To synthesize various pyrrolizidine alkaloids, Padwa’s group used the intramolecular photocycloaddition of N-but-3-enyl-5-thiopyrrolidin-2-ones 338. The intramolecular photo [2 + 2] cycloadditions first generated the tricyclic thietanes 339, which further

Synthesis of carbohydrate-scaffolded thymine glycoconjugates to organize multivalency

• Anna K. Ciuk and
• Thisbe K. Lindhorst

Beilstein J. Org. Chem. 2015, 11, 668–674, doi:10.3762/bjoc.11.75

• water solubility. Then [2 + 2] photocycloaddition was tested. For irradiation the divalent thymine glycoconjugate 7 was diluted (maximum concentration was 500 μg/1 mL) in a 1:1-mixture of water and acetone in order to favor intramolecular photocycloaddition and avoid the intermolecular reaction. Acetone

• glycothymine branches in 13 and 14 are sterically more hindered than the thymine branches in 7 and 8. Again UV–vis spectroscopy further underlines the dimerization success as the absorption maximum at 270 nm disappears and mass spectrometry supports intramolecular photocycloaddition only (cf. Supporting

• ppm). The anomeric H-1 region is detailed in both cases: four new signals are seen in 14 (B) (blue arrows) corresponding to four different isomeric products of the photocycloaddition. Synthesis of carbohydrate-scaffolded dimeric thymine 7 and intramolecular photocycloaddition. The irradiation product

Photochemical approach to functionalized benzobicyclo[3.2.1]octene structures via fused oxazoline derivatives from 4- and 5-(o-vinylstyryl)oxazoles

• Ivana Šagud,
• Simona Božić,
• Željko Marinić and
• Marija Šindler-Kulyk

Beilstein J. Org. Chem. 2014, 10, 2222–2229, doi:10.3762/bjoc.10.230

• )oxazole small quantities of electrocyclization product, 4-(1,2-dihydronaphthalen-2-yl)oxazole, are isolated and spectroscopically characterized. Keywords: bicyclo[3.2.1]octane; intramolecular photocycloaddition; oxazole; styryl; vinyl; Introduction The bicyclo[3.2.1]octane skeleton is the basic

• ][23][24][25]. There are examples of oxazole photochemical intermolecular cycloadditions [26][27][28][29][30][31][32], but to the best of our knowledge, there are no examples of intramolecular photocycloaddition. We describe herein, the synthesis of new 4- and 5-(2-vinylstyryl)oxazoles (1, 2) and their

• intramolecular photocycloaddition to diverse fused tetracyclic oxazoline compounds which further spontaneously or during the work-up procedure hydrolyze to benzobicyclo[3.2.1]octenone derivatives. This is a new method for the synthesis of functionalized benzobicyclo[3.2.1]octenes. Results and Discussion cis

The arene–alkene photocycloaddition

• Ursula Streit and
• Christian G. Bochet

Beilstein J. Org. Chem. 2011, 7, 525–542, doi:10.3762/bjoc.7.61

• -dimensional chiral molecules. It is therefore not surprising that many attempts have been made to render this process enantioselective. The main strategy in this perspective is the introduction of a chiral center directly on the tether in an intramolecular photocycloaddition, and to carry out the reaction in

• the intramolecular photocycloaddition of a cinnamoylamide and a benzamide moiety (Scheme 32) [97]. This reaction is very efficient and leads to high yields of the bicyclo[2.2.2]octadiene derivative. In this example, the cinnamoylamide is sensitized by benzil to its triplet excited-state. The proposed

• dianthryls. Photocycloaddition of enone with benzene. Intramolecular photocycloaddition affording multicyclic compounds via [4 + 2]. Photocycloaddition described by Sakamoto et al. Proposed mechanism by Sakamoto et al. Photocycloaddition described by Jones et al. Proposed mechanism for the formation of

Total synthesis of (±)-coerulescine and (±)-horsfiline

• Mukund G. Kulkarni,
• Attrimuni P. Dhondge,
• Sanjay W. Chavhan,
• Ajit S. Borhade,
• Yunnus B. Shaikh,
• Deekshaputra R. Birhade,
• Mayur P. Desai and
• Nagorao R. Dhatrak

Beilstein J. Org. Chem. 2010, 6, 876–879, doi:10.3762/bjoc.6.103

• [31], dimethyldioxirane (DMDO) mediated oxidation [32], and by tandem intramolecular photocycloaddition–retro-Mannich reaction [33]. The Wittig olefination–Claisen rearrangement protocol [35] provides a ready access to 4-pentenals, which have served as versatile intermediates for the synthesis of a

Reversible intramolecular photocycloaddition of a bis(9-anthrylbutadienyl)paracyclophane – an inverse photochromic system. (Photoactive cyclophanes 5)

• Henning Hopf,
• Christian Beck,
• Jean-Pierre Desvergne,
• Henri Bouas-Laurent,
• Peter G. Jones and
• Ludger Ernst

Beilstein J. Org. Chem. 2009, 5, No. 20, doi:10.3762/bjoc.5.20