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Contemporary Organosilicon Chemistry Contemporary organosilicon chemistry Edited by Steve Marsden Generated on 05 October 2021, 02:13 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. Contemporary organosilicon chemistry Steve Marsden Editorial Open Access Address: Beilstein Journal of Organic Chemistry 2007, 3, No. 4. School of Chemistry, University of Leeds, Leeds LS2 9JT, UK doi:10.1186/1860-5397-3-4 Email: Received: 06 February 2007 Steve Marsden - [email protected] Accepted: 08 February 2007 Published: 08 February 2007 © 2007 Marsden; licensee Beilstein-Institut License and terms: see end of document. Abstract Editorial for the Thematic Series on Contemporary Organosilicon Chemistry. The field of organosilicon chemistry has a rich and varied the 1990s, and equivalent to the number appearing in the much history, and has long since made the progression from chemical longer established field of organoboron chemistry [2]. This esoterica to its position as a mainstay of modern synthetic expansion in activity reflects not only the sustained popularity chemistry. In his 1980 Tilden lectures [1], Professor Ian of traditional silicon-based reactions and reagents, but also Fleming of Cambridge University, himself one of the major newer departures such as the effective application of organosil- practitioners of the discipline, identified the year 1968 as a icon compounds in transition metal-catalysed cross-coupling watershed in the popularisation of organosilicon chemistry. reactions, and the use of silanes as stoichiometric reductants in Notwithstanding the earlier, pioneering work of chemists such a range of chemo-, stereo- and enantioselective catalytic reduc- as Eaborn, 1968 was notable for many innovations we now tions. take for granted, including the development of silyl enol ether chemistry by Stork and Hudrlik, and the eponymous olefination It is therefore a pleasure to serve as Guest Editor for this first reaction by Peterson. These landmark papers triggered a "Thematic Series" in the Beilstein Journal of Organic Chem- massive growth in interest in the area which continues to this istry, on "Contemporary Organosilicon Chemistry". We have day. contributions from some of the leading practitioners in the area, covering a wide range of topics including the stereoselective Nearly 40 years on from those landmark publications, one construction of oxygen and nitrogen-containing heterocycles, could be forgiven for assuming that organosilicon chemistry the use of tethered silicon reagents to deliver acyclic stereocon- has reached such a state of maturity that there remain few areas trol, chiral-at-silicon reagents for asymmetric synthesis, and a ripe for new development. A brief survey of the modern liter- new method for the electrochemical generation of silyl cations. ature quickly dispels this notion. Far from atrophying, organo- Additionally, the unique nature of internet-based publishing silicon chemistry continues to be an area of expansion, with an means that the Series can grow as additional contributions are average of over 550 papers being published per year in the received: future papers in areas including allylation chemistry, decade to date – an increase of over 30% by comparison with stereoselective fluorination, cyclopropane chemistry and the Page 1 of 2 (page number not for citation purposes) Beilstein Journal of Organic Chemistry 2007, 3, No. 4. development of silicon-containing drug candidates should be available shortly. Be sure to check back to keep abreast of the latest developments as the Series grows. Steve Marsden Guest Editor References 1. Fleming, I. Chem. Soc. Rev. 1981, 10, 83–111. doi:10.1039/ cs9811000083 2. Search on ISI Web of Science for articles related to organic chemistry with search terms "silicon or silyl or silane", versus "boron or borane or boronyl or boronic or Suzuki" records 3,871 hits for the former and 3,884 for the latter in the period 2000–2006. 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:10.1186/1860-5397-3-4 Page 2 of 2 (page number not for citation purposes) Reaction of benzoxasilocines with aromatic aldehydes: Synthesis of homopterocarpans Míriam Álvarez-Corral, Cristóbal López-Sánchez, Leticia Jiménez-González, Antonio Rosales, Manuel Muñoz-Dorado and Ignacio Rodríguez-García* Full Research Paper Open Access Address: Beilstein Journal of Organic Chemistry 2007, 3, No. 5. Dpto. Química Orgánica, Universidad de Almería, 04120-Almería, doi:10.1186/1860-5397-3-5 Spain Received: 24 November 2006 Email: Accepted: 08 February 2007 Míriam Álvarez-Corral - [email protected]; Cristóbal López-Sánchez - Published: 08 February 2007 [email protected]; Leticia Jiménez-González - [email protected]; Antonio Rosales - [email protected]; Manuel Muñoz-Dorado - © 2007 Álvarez-Corral et al; licensee Beilstein-Institut. [email protected]; Ignacio Rodríguez-García* - [email protected] License and terms: see end of document. * Corresponding author Abstract Condensation of 2H-benzo[g][1,2]oxasilocines with aromatic aldehydes in the presence of boron trifluoride affords mixtures of cis/ trans 2-phenyl-3-vinylchromans with moderate yields. These can be transformed into homopterocarpans, a synthetic group of substances homologous to the natural isoflavonoid pterocarpans. Background The Sakurai-Hosomi is a useful variant of allylation reactions, ulated by their interesting biological activities, like antitumor [1] which has been used for the formation of carbo- and hetero- [14] or potential anti-HIV. [15] A theoretical study of their cycles. [2,3] We have applied it to the stereoselective synthesis structure has also been published. [16] Here we describe a of dihydrobenzofurans by means of the condensation of concise and convergent approach to this skeleton (1) based on a benzoxasilepines with aromatic aldehydes in the presence of Sakurai condensation between a benzoxasilocine (2) and a Lewis acids. [4,5] Using this methodology and through conver- protected ortho-hydroxybenzaldehyde (Scheme 1). gent synthetic routes, we have prepared pterocarpans [6] and neolignans. [7] These good results have encouraged us to under- Results and discussion take the extension of the method to the use of benzo [g][1,2] Starting materials oxasilocines for the preparation of chromans. This heterocyclic The starting material required for this synthesis is the novel system constitutes the core skeleton of several biologically heterocycle 3,6-dihydro-2,2-dimethyl-2H-benzo [g][1,2]oxasi- active natural products [8-11] and it is also present in the basic locine (5), which can be prepared through ring closing meta- structure of the homopterocarpans. [12] These are a group of thesis (RCM), as has been previously reported for the non- non natural substances whose total synthesis [13] has been stim- benzofused system. [17-19] Thus, silylation of 2-allylphenol Page 1 of 4 (page number not for citation purposes) Beilstein Journal of Organic Chemistry 2007, 3, No. 5. Table 1: Condensation of substituted benzaldehydes with 5. b c benzaldehyde product diastereomeric ratio yield (DCM) yield (CHCl3) substituent (cis/trans)a H 7a 1 : 3 49 56 2-OMe 7b 1 : 1 51 58 3-OMe 7c 1 : 3 30 36 4-OMe 7d 1 : 5 48 60 2-OPiv 7e 1 : 3 48 62 3-OPiv 7f 1 : 5 42 44 4-OPiv 7g 1 : 3 47 58 a: As deduced by analysis of 1H NMR spectra or after CC separation b: reflux; c: 20°C. to perform the condensation with aromatic aldehydes to generate the dihydrobenzofuran final products in the presence of a second equivalent of BF3·Et2O. In a similar way, when 5 is treated with BF3·Et2O in MeOH, the fluorinated species 6 is formed quantitatively (Scheme 3). The 1H NMR is very similar to that of the starting material, but for the methyl groups on silicon, which appear now as doublets due to their coupling 19 3 with the F ( JH-F = 7.3 Hz). This coupling is also observed for the methylene on silicon H4', which exhibits now an addi- 3 tional splitting ( JH-F = 6.5 Hz) (for details see Supporting Information File 1). 13C NMR also reveals the presence of the fluorine on the silicon, because the signal due to the methyl 2 groups appears as a doublet ( JC-F = 14.8 Hz) as well as the Scheme 1: Retrosynthetic analysis for the homopterocarpan skeleton. 2 19 signal due to C4' ( JC-F = 13.5 Hz). F NMR shows only one 3 3 signal at -160.73 ppm (hept t, JF-H = 7.3 Hz, JF-H = 6.5 Hz) 19 29 2 (3) (or conveniently functionalized derivatives) with allyl- with satellite bands due to the F- Si coupling ( JF-Si = 283 chlorodimethylsilane followed by RCM with 2nd generation Hz). A similar spectroscopic behaviour has been reported for Grubbs catalyst [20] leads to the cyclic siloxane with high other fluorosilanes. [4,21] yields (Scheme 2). The good results in the cyclization step make this approach an excellent way of synthesising of this heterocycle. Scheme 2: Reagents: i CH2 = CHCH2SiMe2Cl, Et3N, DCM, 85%; ii 2nd generation Grubbs catalyst, DCM, 91%.
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