“…Thus, the desired cyclobutarene 17 could not be isolated when α,α-dimethyl sulfone 15 was treated with fluoride. In this case, only 16 could be isolated (eq 2) …”
Section: Synthesismentioning
confidence: 99%
“…In this case, only 16 could be isolated (eq 2). 22 The sterically congested benzene derivative 18 23 has been converted thermally into the cyclobutarene 20 in nearly quantitative yield. The facile elimination of HCl from 18 may be attributed to steric strain in 18, 24 whereas stabilization of the four-membered ring in 20 probably results from the buttressing effect of the aromatic ring substituents (Scheme 3).…”
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.
“…Thus, the desired cyclobutarene 17 could not be isolated when α,α-dimethyl sulfone 15 was treated with fluoride. In this case, only 16 could be isolated (eq 2) …”
Section: Synthesismentioning
confidence: 99%
“…In this case, only 16 could be isolated (eq 2). 22 The sterically congested benzene derivative 18 23 has been converted thermally into the cyclobutarene 20 in nearly quantitative yield. The facile elimination of HCl from 18 may be attributed to steric strain in 18, 24 whereas stabilization of the four-membered ring in 20 probably results from the buttressing effect of the aromatic ring substituents (Scheme 3).…”
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.
“…Due to the thermodynamic stability associated with the aromatic system and the kinetic reactivity of the strained cyclobutene ring (Cava and Napier, 1956; Mehta and Kotha, 2001), these molecules behave as reliable and synthetically useful feedstocks (Christophe et al, 1998) and have been extensively applied in natural product syntheses (Funk and Vollhardt, 1977, 1979; Grieco et al, 1980; Taber et al, 1987; Nemoto et al, 1995; Michellys et al, 2001). With these contributions in mind, great efforts to establish synthetic protocols for cyclobutarene synthesis have been developed which include 1,4-elimination-cycloaddition of functionalized arenes (Gray et al, 1978; Schirch et al, 1979; Sekine et al, 1979; Lenihan and Shechter, 1994, 1998; Chou et al, 1995), Parham cyclization (Bradsher and Hunt, 1981; Buchwald et al, 1987a,b; Beak and Selling, 1989; Aidhen and Ahuja, 1992), photo-induced cycloadditions (Parham et al, 1976; Kaneko and Naito, 1979; Neckers and Wagenaar, 1981; Kaneko et al, 1982; Kanao et al, 1983; Sato et al, 1987; Hoffmann and Pete, 1996), thermal extrusion reactions (Toda et al, 1988; D'Andrea et al, 1990; Hickman et al, 1991; Shimada et al, 1993; Andersen et al, 1996; Craig et al, 1998), intramolecular addition of carbanions to benzynes (Bunnett and Skorcz, 1962; Krohn et al, 1978; Gowland and Durst, 1979), [2 + 2 + 2] cycloadditions of 1,5-hexadiyne (Peter and Vollhardt, 1977, 1984; Funk and Vollhardt, 1980; McNichols and Stang, 1992), ring expansion of cycloproparenes (Birch et al, 1964; Iskander and Stansfield, 1965; Buckland et al, 1987; Kagabu and Saito, 1988; Müller et al, 1989), and [2 + 2] cycloadditions of allene precursors (Inanaga et al, 1992; Ezcurra and Moore, 1993; Toda et al, 1994) and other methods (Markgraf et al, 1969; Garratt and Nicolaides, 1972, 1974; Bilyard et al, 1979; Warrener et al, 1993). However, these methods encounter some drawbacks such as high temperatures (400°C-800°C), strong bases ( n -BuLi and NaNH 2 ), multiple steps, or a narrow substrate range.…”
A new Fe(III)-catalyzed bicyclization reaction of yne-allenones with indoles has been established, enabling the direct construction of cyclobuta[a]naphthalen-4-ols with an all-carbon quaternary center in good to excellent yields. This reaction was performed by using low-cost FeCl3 as the catalyst and EtOH as the environmentally benign solvent, providing a green protocol for constructing the cyclobutarene framework with a high degree of atom economy and functional group compatibility. The reaction mechanism was proposed to proceed through a [2 + 2] cycloaddition/1,6-conjugate addition cascade.
The benzocyclobutene (BCB) moiety is present in several bioactive natural products and medicinally interesting molecules. BCB is also a valuable synthon for building a variety of polymers by the virtue of its propensity to undergo polymerization. The research on BCB chemistry has grown in the last few decades due to its unique applications in various fields of science. In this review, we have included various methods for the preparation of BCBs and highlighted their applications in the construction of diverse complex structural frameworks. We believe that this review will be useful to synthetic chemists and polymer scientists, and we anticipate several new applications will emerge in this promising area.Scheme 1. Dihalocarbene insertion to substituted benzocyclopropenes.
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