“…As seen in Figure , a powerful extension of this benzannulation methodology would be its intramolecular variant (IMPEDA). No example of IMPEDA reaction involving an all-carbon tether between the reacting functionalities (e.g., 34 ; Figure ) had been reported at the outset of this work, and it was clear that the successful implementation of such synthetic technology would provide a useful entry into complex polycycles of the general form 36 . To ascertain the viability of this proposal, we proceeded to access the requisite photocyclization precursors 46a − f , 47a − f , 48a − f , and 52 − 54 via a general and efficient route (Schemes and ).…”
A number of naturally occurring substances, including hamigerans, contain ring systems which are fused to an aromatic nucleus. A general and streamlined method for the construction of such benzannulated bi- and polycyclic carbon frameworks has been developed, and its scope and limitations were explored. On the basis of the photoenolization of substituted benzaldehydes and subsequent Diels-Alder (PEDA) trapping of the generated hydroxy-o-quinodimethanes, this method was optimized to set the stage for the total synthesis of several naturally occurring members of the hamigeran class. Specifically, the developed synthetic technology served as the centerpiece process for the successful asymmetric synthesis of hamigerans A (2), B (3), and E (7). In addition to the PEDA reactions, several other novel reaction processes are described, including a high-yielding decarbonylative ring contraction and an oxidative decarboxylation of a hydroxyl beta-keto ester to afford an alpha-diketone. A number of analogues of these biologically active natural products were also prepared by application of the developed technology.
“…As seen in Figure , a powerful extension of this benzannulation methodology would be its intramolecular variant (IMPEDA). No example of IMPEDA reaction involving an all-carbon tether between the reacting functionalities (e.g., 34 ; Figure ) had been reported at the outset of this work, and it was clear that the successful implementation of such synthetic technology would provide a useful entry into complex polycycles of the general form 36 . To ascertain the viability of this proposal, we proceeded to access the requisite photocyclization precursors 46a − f , 47a − f , 48a − f , and 52 − 54 via a general and efficient route (Schemes and ).…”
A number of naturally occurring substances, including hamigerans, contain ring systems which are fused to an aromatic nucleus. A general and streamlined method for the construction of such benzannulated bi- and polycyclic carbon frameworks has been developed, and its scope and limitations were explored. On the basis of the photoenolization of substituted benzaldehydes and subsequent Diels-Alder (PEDA) trapping of the generated hydroxy-o-quinodimethanes, this method was optimized to set the stage for the total synthesis of several naturally occurring members of the hamigeran class. Specifically, the developed synthetic technology served as the centerpiece process for the successful asymmetric synthesis of hamigerans A (2), B (3), and E (7). In addition to the PEDA reactions, several other novel reaction processes are described, including a high-yielding decarbonylative ring contraction and an oxidative decarboxylation of a hydroxyl beta-keto ester to afford an alpha-diketone. A number of analogues of these biologically active natural products were also prepared by application of the developed technology.
“…Upon thermal activation, the benzocyclobutenyl ketone oximes 465 gave 3,4-disubstituted isoquinolines 467 via o -quinodimethane intermediate 466 (Scheme ) . Several additional examples of related pericyclic reactions have been reported. ,− 104 …”
Section: Other Pericyclic Reactionsmentioning
confidence: 99%
“…355 Several additional examples of related pericyclic reactions have been reported. 347,[356][357][358]…”
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.
“…spectrum of compound (2) yielded the values of J1,9a, JlV9p, J1,6, and as 4, 7, 9, and ca. 0 Hz, respectively, consistent with the half-boat conformation in which the corresponding dihedral angles are tion gave two products, with RF values of 0.47 and 0.61, in the ratio of 4 : 1, which were separated by column chromatography and identified spectroscopically as compounds (4) and (5). The trans-fused racemate (5) can only adopt a single, rigid conformation.…”
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