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Photocycloadditions and Photorearrangements Photocycloadditions and photorearrangements Edited by Axel G. Griesbeck Generated on 04 October 2021, 00:16 Imprint Beilstein Journal of Organic Chemistry www.bjoc.org ISSN 1860-5397 Email: [email protected] The Beilstein Journal of Organic Chemistry is published by the Beilstein-Institut zur Förderung der Chemischen Wissenschaften. This thematic issue, published in the Beilstein Beilstein-Institut zur Förderung der Journal of Organic Chemistry, is copyright the Chemischen Wissenschaften Beilstein-Institut zur Förderung der Chemischen Trakehner Straße 7–9 Wissenschaften. The copyright of the individual 60487 Frankfurt am Main articles in this document is the property of their Germany respective authors, subject to a Creative www.beilstein-institut.de Commons Attribution (CC-BY) license. Photocycloadditions and photorearrangements Axel G. Griesbeck Editorial Open Access Address: Beilstein J. Org. Chem. 2011, 7, 111–112. University of Cologne, Department of Chemistry, Organic Chemistry, doi:10.3762/bjoc.7.15 Greinstr. 4, D-50939 Köln, Germany; Fax: +49(221)470 5057 Received: 15 December 2010 Email: Accepted: 04 January 2011 Axel G. Griesbeck - [email protected] Published: 26 January 2011 This article is part of the Thematic Series "Photocycloadditions and photorearrangements". Guest Editor: A. G. Griesbeck © 2011 Griesbeck; licensee Beilstein-Institut. License and terms: see end of document. Organic synthesis using light as reagent and producing com- Photocycloaddition reactions can be performed in numerous plex molecules from simple starting materials is realized in ways using unsaturated substrates such as carbonyl compounds, exemplary fashion in natural photosynthesis. Mankind still Michael acceptors, monoalkenes, polyenes, or aromatic struggles for an efficient molecular system that mimics this substrates leading to complex products that can be used in natural process. In order to harvest light energy and to trans- subsequent transformations. The carbonyl-ene photocycloaddi- form it into chemical energy, photochemical reactions must be tion, for example, is an important route to oxetanes, products studied and optimized for synthetic applications. Two major that have recently gained increasing attention as building blocks reaction paths that use electronic excitation are photocycloaddi- in organic synthesis as well as in materials science [1]. Photo- tions and photochemical rearrangements. These reactions have chemical rearrangements are impressive reactions with regard to been intensively investigated in recent decades in terms of the generation of complexity: 1,2- and 1,3-acyl shifts are known regio-, stereo-, spin- and (electronic) configurational selectivi- from carbonyl photochemistry, di-π-methane and oxa-di-π- ties. methane rearrangements are processes that can occur with a remarkable increase in molecular and stereochemical complexi- Prior to every photochemical reaction, an electronically excited ty, as can meta arene photocycloadditions. state is generated either by direct light absorption or by energy transfer sensitization. This excited state has to be sufficiently It was a great pleasure to act as the editor of this Thematic well characterized in order to understand its chemical and phys- Series on photochemical reactions and I would like to thank all ical behaviour. Organic molecules can react either as triplet or authors for their excellent contributions and the staff of the singlet excited states, often showing spin-specific reactivities Beilstein-Institut for their support. and selectivities. Additionally, the nature of the excited state, as characterized by the state configuration, is crucial for the re- Axel G. Griesbeck activity of the molecule, for example, nπ* states favour hydrogen abstraction and addition modes whereas ππ* states Cologne, January 2011 favour addition and electron transfer modes. 111 Beilstein J. Org. Chem. 2011, 7, 111–112. Reference 1. Burkhard, J. A.; Wuitschik, G.; Rogers-Evans, M.; Müller, K.; Carreira, E. M. Angew. Chem., Int. Ed. 2010, 49, 9052–9067. doi:10.1002/anie.200907155 License and Terms This is an Open Access article under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The license is subject to the Beilstein Journal of Organic Chemistry terms and conditions: (http://www.beilstein-journals.org/bjoc) The definitive version of this article is the electronic one which can be found at: doi:10.3762/bjoc.7.15 112 Synthesis of 2a,8b-Dihydrocyclobuta[a]naphthalene- 3,4-diones Kerstin Schmidt and Paul Margaretha* Full Research Paper Open Access Address: Beilstein J. Org. Chem. 2010, 6, No. 76. doi:10.3762/bjoc.6.76 Chemistry Department, University of Hamburg, Martin-Luther-King Platz 6, D-20146 Hamburg, Germany Received: 07 May 2010 Accepted: 02 July 2010 Email: Published: 13 July 2010 Paul Margaretha* - [email protected] Guest Editor: A. G. Griesbeck * Corresponding author © 2010 Schmidt and Margaretha; licensee Beilstein-Institut. Keywords: License and terms: see end of document. cyclobutenes; photocycloaddition; quinone monoacetals Abstract On irradiation (λ = 350 nm) in neat hex-1-yne, naphthalene-1,2-dione monoacetals 1 afford mixtures of pentacyclic photodimers and up to 25% (isolated yield) of mixed photocycloadducts 2. Careful acidic hydrolysis of the acetal function of 2 gives the title compounds 3, the overall sequence representing a first approach to a (formal) [2 + 2] photocycloadduct of a 1,2-naphthoquinone to an alkyne. Introduction The behaviour of excited 1,2- and 1,4-quinones towards enone + alkyne cycloadducts as indicated by 1H NMR spectro- ground-state molecules differs greatly. Whereas the former scopy. The yields of mixed cycloadducts with many alkynes typically react via H-abstraction by an excited carbonyl group (3,3-dimethylbut-1-yne, trimethylsilylacetylene, 3-[(trimethyl- [1], the latter smoothly undergo [2 + 2] cycloaddition to alkenes silyl)oxy]prop-1-yne or hex-3-yne were invariably low (<5%). to afford cyclobutane-type products [2]. Very recently we Moderately higher yields (15–25%) were obtained using hex-1- reported the use of 1,2-dihydro-1,1-dimethoxynaphthalen-2- yne in either benzene or acetonitrile as solvent. Best results ones 1 as protected precursors for the synthesis of both photo- were obtained using hex-1-yne, both as reaction partner and as cyclodimers and ketene-photocycloadducts of 1,2-naphto- solvent. Thus, irradiation of either 1a or 1b in neat hex-1-yne quinones [3,4]. Here we report the preparation of – novel – affords a mixture of the corresponding dimeric dibenzo- 2a,8b-dihydrocyclobuta[a]naphthalene-3,4-diones, i.e. (formal) phenylenediones (two regioisomers [3], 67–70%) and up to 1,2-naphthoquinone + alkyne [2 + 2] cycloadducts. 30–33% of cycloadducts 2a or 2b, respectively. Compounds 2 can easily be isolated by chromatography (25% isolated yield) Results as they exhibit much higher Rf-values than the corresponding Irradiation of 1 in the presence of alkynes affords the – known dimers. In contrast, naphthalenone 1c under the same condi- [3] – pentacyclic dimers and variable amounts (0–33%) of tions only affords <5% of 2c. Hydrolysis of cycloadducts 2 in a Page 1 of 3 (page number not for citation purposes) Beilstein J. Org. Chem. 2010, 6, No. 76. two phase mixture (CH2Cl2, aq HCl) at r.t. [5] leads to quanti- photoreactor equipped with (16) 350 nm lamps. Column tative deprotection of the acetal function as indicated by 1H chromatography (CC) was carried out with silica gel 60 (Merck; NMR spectroscopy to afford compounds 3a or 3b, respectively 230–400 mesh). 1H and 13C NMR spectra (including 2D plots) (Scheme 1). Compounds 3 are also easy to purify by were recorded with a Bruker WM-500 instrument at 500.13 and chromatography (83–85% isolated yield) which is greatly 125.8 MHz, resp., in CDCl3, δ in ppm, J in Hz. assisted by the fact that they are easily detectable on account of their yellow colour. 2. Photolyses. Ar-Degassed solns. of 1 (1 mmol) in hex-1-yne (10 ml) were irradiated for 15 h up to total conversion (moni- toring by TLC). After evaporation of the excess alkyne, the crude mixtures were analyzed by 1H NMR in order to deter- mine the crude yield. CC (SiO2, pentane/Et2O 6:1) gave the photocycloadducts 2. 1-Butyl-3,4-dihydro-4,4-dimethoxy- 2aH,8bH-cyclo-buta[a]naphthalen-3-one (2a): 72 mg (25%), 1 colourless oil, Rf = 0.65. H NMR: 7.70 (d, J = 8.4, 1H); 7.36 (t, J = 8.4, 1H); 7.30 (m, 2H); 5.97 (s, 1H); 4.52 (d, J = 4.6, 1H); 4.00 (bs, 1H); 3.53 & 3.00 (s, 3H); 2.16 (t, J = 7.0, 2H); 1.52 (m, 2H); 1.38 (m, 2H); 0.92 (t, J = 6.9, 3H). 13C NMR: 203.1 (s); 156.2 (s); 137.3 (s); 134.5 (s); 129.1 (d); 128.6 (d); 128.4 (d); 127.8 (d); 125.2 (d); 99.1 (s); 51.0 (q); 50.1 (d); 49.2 (q); 48.3 (d); 30.2 (t); 28.6 (t); 22.5 (t); 14.2 (q). Anal. Calcd for C18H22O3: C, 75.50; H, 7.74. Found: C, 75.43; H, 7.78. 7-Bromo-1-butyl-3,4-dihydro-4,4-dimethoxy-2aH,8bH-cyclo- Scheme 1: Synthesis of 2a,8b-dihydrocyclobuta[a]naphthalene-3,4- buta[a]naphthalen-3-one (2b): 91 mg (25%), light yellow solid, diones. 1 m.p. 50 – 52 °C, Rf = 0.61. H NMR: 7.55 (d, J = 8.4, 1H); 7.42 (s, 1H); 7.41 (d, J = 8.4, 1H); 5.96 (s, 1H); 4.46 (d, J = 4.6, 1H); Discussion 3.95 (bs, 1H); 3.52 & 2.97 (s, 3H); 2.16 (t, J = 7.0, 2H); 1.52 At first glance, the (relatively) low yield of mixed cycloadduct (m, 2H); 1.38 (m, 2H); 0.93 (t, J = 6.9, 3H).
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