Polyhalogenierte Bicyclo[4.2.0]octa‐1,5,7‐triene, VIII. Synthese und Cyclodimerisierung von polyhalogenierten 2‐Phenyl‐ und 2‐Pentachlorphenyl‐substituierten Buteninen
Abstract:Eingegangen am 12. Dezember 1980Herrn Prof. Dr. Siedried Hiinig zum 60. Geburtstag gewidmet.Ausgangsmaterial fur die Synthese der Butenine l c -e ist der Aldehyd 4, der uber 9 oder 5 und 10 in l c bzw. iiber 8 in 1 d ubergefuhrt werden kann. In der vierstufigen Synthese von l e ist der entscheidende Reaktionsschritt die Perchlorierung des Phenylkerns von 6 zu 7 mit dem BallesterReagenz. Starting material for the synthesis of the butenynes l c -e is the aldehyde 4 which can be converted into l c via 9 or 5 and … Show more
“…The α-dimers can also be converted to β-dimers at 120−180 °C. Benzocyclobutenes 300a − f can be further hydrolyzed by sulfuric acid or silver trifluoroacetate to give substituted benzocyclobutenediones 301a − f (Scheme , Table ). − 68 …”
“…Benzocyclobutenes 300a-f can be further hydrolyzed by sulfuric acid or silver trifluoroacetate to give substituted benzocyclobutenediones 301a-f (Scheme 68, Table 9). [180][181][182][183][184] Phthalazine-1,4-dione 304 can be generated readily in solution by oxidation of 302. Although the hydrazide is a labile species that polymerizes on attempted isolation, it adds rapidly to dienes, forming stable Diels-Alder adducts.…”
A general method for the synthesis of cyclobutarenes involves 1,4-elimination from adjacent benzylic positions, followed by ring closure of the resulting o-quinodimethane. The earliest report in which an o-quinodimethane was implicated was the reaction of R,R,R′,R′-tetrabromo-o-xylene (4) with iodide to give the 1,2-dibromocyclobutarene 6, via o-quinodimethane 5. Treatment of 6 with NaI in acetone gave diiodide 7, which on catalytic reduction gave 1 (Scheme 1). [15][16][17] Cava and co-workers confirmed that 5 was an intermediate by trapping experiments using sev-eral dienophiles. 18 A similar procedure has been used to prepare 1,2-diphenylcyclobutarene. 19 Heterocyclic analogues may also be prepared by the 1,4-elimination of halogen from suitable precursors. Compounds 9 and 11 have been synthesized from 8 and 10, respectively, as illustrated in Scheme 2. 20 A variation of the method involves the conversion of R-alkyl-R-bromosulfones into cyclobutarenes using tetrabutylammonium fluoride (TBAF) in acetonitrile at 20-25 °C to effect the elimination. 21 The desired cyclobutarene is often accompanied by olefinic side products, as illustrated in the preparation of cyclobutarene 13, which is accompanied by 14 (eq 1) (Table 1). Anil K. Sadana was born in Panipat, India. He did his M.Sc (1990) and M. Phil (1992) from Kurukshetra University, India. He obtained his Ph.D. degree in 1999 under the guidance of Prof. Om Prakash. His Ph.D. work focused on the utility of hypervalentiodine reagents in the synthesis of heterocyclic compounds. He then joined Prof. W. E. Billups lab as postdoctoral research associate in 2000. He is presently working on small ring compounds and carbon nanotubes. Rajesh Kumar Saini was born in 1966 in Ambala, India. He received his masters degree in 1989 and his Ph.D. in 1996 from Kurukshetra University, India. After his doctorate he moved to the United States for his postdoctoral studies. After a brief stay at Sam Houston State University he joined Rice University, where he is working as a Research Scientist in the laboratories of Prof. W. E. Billups and Prof. Richard E. Smalley. His research has concentrated on small ring compound and the development of carbon nanotube chemistry. W. E. Billups was born in 1939 in Huntington, West Virginia. He received his B.S. in Chemistry Degree from Marshall University in 1961. This was followed by a period in industry after which he entered the graduate school of the Pennsylvania State University in 1968 and received the Ph.D. in 1970. He then joined the chemistry department at Rice University. He served as the Department Chair from July 1985 until December 1991. His research interests are divided among the areas of small-ring compounds, reactive intermediates, chemistry of free metal atoms and more recently fullerene and carbon nanotube chemistry.
“…The α-dimers can also be converted to β-dimers at 120−180 °C. Benzocyclobutenes 300a − f can be further hydrolyzed by sulfuric acid or silver trifluoroacetate to give substituted benzocyclobutenediones 301a − f (Scheme , Table ). − 68 …”
“…Benzocyclobutenes 300a-f can be further hydrolyzed by sulfuric acid or silver trifluoroacetate to give substituted benzocyclobutenediones 301a-f (Scheme 68, Table 9). [180][181][182][183][184] Phthalazine-1,4-dione 304 can be generated readily in solution by oxidation of 302. Although the hydrazide is a labile species that polymerizes on attempted isolation, it adds rapidly to dienes, forming stable Diels-Alder adducts.…”
A general method for the synthesis of cyclobutarenes involves 1,4-elimination from adjacent benzylic positions, followed by ring closure of the resulting o-quinodimethane. The earliest report in which an o-quinodimethane was implicated was the reaction of R,R,R′,R′-tetrabromo-o-xylene (4) with iodide to give the 1,2-dibromocyclobutarene 6, via o-quinodimethane 5. Treatment of 6 with NaI in acetone gave diiodide 7, which on catalytic reduction gave 1 (Scheme 1). [15][16][17] Cava and co-workers confirmed that 5 was an intermediate by trapping experiments using sev-eral dienophiles. 18 A similar procedure has been used to prepare 1,2-diphenylcyclobutarene. 19 Heterocyclic analogues may also be prepared by the 1,4-elimination of halogen from suitable precursors. Compounds 9 and 11 have been synthesized from 8 and 10, respectively, as illustrated in Scheme 2. 20 A variation of the method involves the conversion of R-alkyl-R-bromosulfones into cyclobutarenes using tetrabutylammonium fluoride (TBAF) in acetonitrile at 20-25 °C to effect the elimination. 21 The desired cyclobutarene is often accompanied by olefinic side products, as illustrated in the preparation of cyclobutarene 13, which is accompanied by 14 (eq 1) (Table 1). Anil K. Sadana was born in Panipat, India. He did his M.Sc (1990) and M. Phil (1992) from Kurukshetra University, India. He obtained his Ph.D. degree in 1999 under the guidance of Prof. Om Prakash. His Ph.D. work focused on the utility of hypervalentiodine reagents in the synthesis of heterocyclic compounds. He then joined Prof. W. E. Billups lab as postdoctoral research associate in 2000. He is presently working on small ring compounds and carbon nanotubes. Rajesh Kumar Saini was born in 1966 in Ambala, India. He received his masters degree in 1989 and his Ph.D. in 1996 from Kurukshetra University, India. After his doctorate he moved to the United States for his postdoctoral studies. After a brief stay at Sam Houston State University he joined Rice University, where he is working as a Research Scientist in the laboratories of Prof. W. E. Billups and Prof. Richard E. Smalley. His research has concentrated on small ring compound and the development of carbon nanotube chemistry. W. E. Billups was born in 1939 in Huntington, West Virginia. He received his B.S. in Chemistry Degree from Marshall University in 1961. This was followed by a period in industry after which he entered the graduate school of the Pennsylvania State University in 1968 and received the Ph.D. in 1970. He then joined the chemistry department at Rice University. He served as the Department Chair from July 1985 until December 1991. His research interests are divided among the areas of small-ring compounds, reactive intermediates, chemistry of free metal atoms and more recently fullerene and carbon nanotube chemistry.
“…Cyclodimerization of polyhalogenated 2-phenyl-and 2-pentachlorophenyl-substituted butenynes 80 under thermal conditions furnishes the bicyclo[4.2.0]octane derivative which can be further hydrolysed/aromatized to the benzocyclobutenones 81 (Scheme 45). 66 An apparently general and regioselective synthesis of substituted benzocyclobutenediones 84 has been reported via palladiumcatalysed coupling of a variety of 4-chlorocyclobutenones 82 with the tributylstannylcyclobutenone derivative 83 followed by hydrolysis (Scheme 46). 67 Some of the BCB derivatives prepared by this route are not accessible by other known routes.…”
The photochemically induced Wolff rearrangement has proved to be an excellent method for the preparation of BCB derivatives-by a ring contraction protocol-which are otherwise dif®cult to prepare. Thus, the a-diazoindanones 48 undergo a ring contraction reaction under a Scheme 13. Scheme 14. Scheme 15. Scheme 16.
“…Scheme 1 meta-Selective arene borylation of 1,3-disubstituted benzene derivative 1 to produce 1,3,5-trisubstituted benzene 2; structure of poipuol (3) The reaction of ketone 7 with diethyl (trichloromethyl)phosphonate and n-butyllithium delivered the desired dichloroolefin 10 (Scheme 4). 6 The following CH-borylation with catalyst system [Ir(cod)(OMe)] 2 /dtbpy/(Bpin) 2 gave arylboronic ester 11 with complete meta-selectivity in very good yield (Scheme 4). An X-ray crystal structure of the product (Figure 1) allowed an unambiguous structural assignment of the borylation product.…”
A synthesis of the marine natural product poipuol is reported. The key reaction sequence consists of an iridium-catalyzed meta-selective CH-borylation followed by the conversion of the resulting arylboronic ester into an aryl chloride.For a long time the direct meta-selective functionalization of benzene derivatives had been restricted to systems carrying electron-withdrawing groups and had been impossible for electron-rich systems. The situation changed with the discovery of iridium-catalyzed CH-borylation of arenes. 1 Miyaura et al. introduced the catalyst system [Ir(cod)Cl] 2 (cod = cyclooctadiene) in combination with 4,4¢-di-tert-butyl-2,2¢-bipyridine (dtbpy) and bis(pinacolato)diboron [(Bpin) 2 ] as borylating reagent. 1a The use of [Ir(cod)(OMe)] 2 allowed an aromatic CH-borylation at room temperature. 1b The regioselectivity of the borylation is directed by steric factors, which lead in the case of a 1,3-disubstituted benzene derivative 1 to the predominant formation of the meta-substitution product 2 (Scheme 1). The synthetic potential of the CH-borylation of arenes was expanded by Maleczka and Smith with the introduction of a C-H activation/borylation/oxidation protocol to produce meta-substituted phenols. 1dTo use this meta-selective aromatic borylation in the complex functional environment of a natural product synthesis, we were interested in the functional tolerance of this reaction. Here, we present first results addressing the point of functional tolerance in the context of a synthesis of the natural product poipuol (3) (Scheme 1). Poipuol (3) was isolated by Sitachitta et al. from the marine sponge Hyrtios sp., collected at a depth of 18 meters near Kauai Island, Hawaii. 2The starting point for the synthesis of the borylation precursor was the aromatic aldehyde 4 (Scheme 2). A Knoevenagel-Doebner reaction 3 of 4 with ethyl butyracetate led to condensation product 5 in nearly quantitative yield. The hydrogenation of 5 gave b-keto ester 6. Treatment of the latter with potassium hydroxide in aqueous ethanol resulted in the formation of ketone 7 (Scheme 2). 4Scheme 2 Reagents and conditions: (a) PrCOCH 2 CO 2 Et, AcOH, piperidine, toluene, reflux; (b) NaOAc, Pd(OH) 2 /C, H 2 , EtOAc; (c) KOH, H 2 O, EtOH, reflux.The CH-borylation of arene 7 in the presence of the catalyst system consisting of 0.75% [Ir(cod)(OMe)] 2 /1.5% dtbpy/(Bpin) 2 (1 equiv) gave arylboronic ester 8 with complete meta selectivity and in very good yield (Scheme 3). In contrast to the low-temperature conditions reported by Miyaura, 1b harsher conditions (microwave, 150°C, 3 h) were necessary for the conversion of 7 into 8. Notable is the compatibility of the ketone function with the borylation conditions. The conversion of 8 into poipuol (3) would require the generation of aryl chloride 9 from the arylboronic ester (Scheme 3). Attempts to use copper(II) chloride 5 for this purpose failed due to side reactions with the ketone. An inseparable mixture of a-chloro ketones was obtained. Therefore, the transformation of ketone 7 into dichl...
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