Polar reactions of acyclic conjugated bisallenes

• Reiner Stamm and
• Henning Hopf

Beilstein J. Org. Chem. 2013, 9, 36–48, doi:10.3762/bjoc.9.5

• − in this case) the (E)-diastereomer 55 results; likewise 53 furnishes the (Z)-isomer 56. From these considerations we would expect 55 to be the dominant product. If 50 loses a proton the butadienylallene 51 results, which by reprotonation at its allene carbon atom, followed by electrocyclization is

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

Beilstein J. Org. Chem. 2012, 8, 1936–1998, doi:10.3762/bjoc.8.225

• bisallenes. After the first isolation of 2 it was quickly demonstrated that on heating (either in solution or in the gas phase) it cyclizes to 3,4-bismethylenecyclobutene (130) in quantitative yield (Scheme 34) [6]. Up to the present day this electrocyclization remains the most thoroughly investigated

• [108][109], Pasto [29][115][116], Skattebøl [117] and others [118]. As shown in Scheme 35, the electrocyclization occurs in a strictly conrotatory manner and the stereoselectivity of the process depends on the steric size of the terminal substituents. For example, bisallene 131 has two distinct

• display anomalies in their bond lengths (Csp2–Csp2 bonds as long as 1.540 Å) [120]. For another route to benzocyclobutenes see Section 2.4, Scheme 71. A most interesting electrocyclization/dimerization process has been discovered by McGlinchey and co-workers for the disilylated hydrocarbon 86 (Scheme 37

Synthesis of a novel chemotype via sequential metal-catalyzed cycloisomerizations

• Bo Leng,
• Stephanie Chichetti,
• Shun Su,
• Aaron B. Beeler and
• John A. Porco Jr.

Beilstein J. Org. Chem. 2012, 8, 1338–1343, doi:10.3762/bjoc.8.153

• with the Pt-activated alkyne, the resulting metal-“ate” intermediate 28 may undergo preferential elimination and proto-demetallation to afford 1,5-diene 29. A second elimination results in the ring-opened triene 30. Subsequent 6π-electrocyclization affords alcohol 31, which aromatizes through loss of

Photoreactions of cyclic sulfite esters: Evidence for diradical intermediates

• Rick C. White,
• Benny E. Arney Jr. and
• Heiko Ihmels

Beilstein J. Org. Chem. 2012, 8, 1208–1212, doi:10.3762/bjoc.8.134

•  3). The cis-stilbene (10) is subsequently transformed into phenanthrene (11) by photoinduced electrocyclization [22] as shown in Scheme 4. Conclusion We have demonstrated that the performance of photoreactions of cyclic sulfites under relatively mild reaction conditions enables the detection of

On the bromination of the dihydroazulene/vinylheptafulvene photo-/thermoswitch

• Virginia Mazzanti,
• Martina Cacciarini,
• Søren L. Broman,
• Christian R. Parker,
• Magnus Schau-Magnussen,
• Andrew D. Bond and
• Mogens B. Nielsen

Beilstein J. Org. Chem. 2012, 8, 958–966, doi:10.3762/bjoc.8.108

• ; photoswitch; vinylheptafulvene; Introduction 1,8a-Dihydroazulene-1,1-dicarbonitrile (DHA, 1) is a yellow photochromic compound, which undergoes a light-induced 10-electron retro-electrocyclization to a red-colored vinylheptafulvene (VHF) (Scheme 1) [1][2][3]. The VHF compound is formed as the s-cis conformer

Continuous flow photolysis of aryl azides: Preparation of 3H-azepinones

• Farhan R. Bou-Hamdan,
• François Lévesque,
• Alexander G. O'Brien and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2011, 7, 1124–1129, doi:10.3762/bjoc.7.129

• increased concomitant formation of the byproduct 10. Lactam 10 was obtained upon re-exposure of purified 9a to the reaction conditions and is believed to result from photochemical disrotatory electrocyclization of the 3H-azepinone diene moiety [51][52][53][54] (Scheme 3). Instead of making a direct

A practical two-step procedure for the preparation of enantiopure pyridines: Multicomponent reactions of alkoxyallenes, nitriles and carboxylic acids followed by a cyclocondensation reaction

• Christian Eidamshaus,
• Roopender Kumar,
• Mrinal K. Bera and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2011, 7, 962–975, doi:10.3762/bjoc.7.108

• , we reported a new synthesis of pyridines based on the trimethylsilyl trifluoromethanesulfonate (TMSOTf) induced cyclocondensation reaction of β-ketoenamides [29][30][31][32][33][34]. This cyclocondensation step can be rationalized as a 6π-electrocyclization of the disilylated intermediate 5 to

An efficient and practical entry to 2-amido-dienes and 3-amido-trienes from allenamides through stereoselective 1,3-hydrogen shifts

• Ryuji Hayashi,
• John B. Feltenberger,
• Andrew G. Lohse,
• Mary C. Walton and
• Richard P. Hsung

Beilstein J. Org. Chem. 2011, 7, 410–420, doi:10.3762/bjoc.7.53

• ][97][98][99]) to access cyclic 2-amido-dienes that are quite rare (for examples see [100][101][102]). Chiral amido-triene 22 underwent electrocyclization efficiently to give chiral cyclic 2-amido-diene 44a in 84% yield. Although obtained in only 35% yield, the achiral cyclic 2-amido-diene 45 could

• (135 °C), thereby implying an accelerated process of electrocyclization. This feature is consistently observed in related ring-closures of 1,3,5-hexatrienes with an electron-donating substituent at the C3 position of the triene [94][95][96][97][98][99] (for theoretical studies on substituent effects on

Expedient syntheses of the N-heterocyclic carbene precursor imidazolium salts IPr·HCl, IMes·HCl and IXy·HCl

• Lukas Hintermann

Beilstein J. Org. Chem. 2007, 3, No. 22, doi:10.1186/1860-5397-3-22

• involving a 1,5-dipolar electrocyclization is proposed. Background Imidazolylidene carbenes have been investigated as ligands in coordination chemistry, as powerful steering/controlling elements in transition-metal catalysis,[1][2] and more recently as metal-free catalysts for organic reactions[3][4]. Some

• can be induced by chloromethylethers. Loss of HCl from B (presumably to A, which is a monobasic species)[13] gives an imino-azomethin-ylide 1,5-dipole C (only one mesomeric structure shown), which will undergo 1,5-dipolar cyclization (6π electrocyclization) [18][19][20] to an oxy-imidazoline D

• full experimental data. The carbenes IPr, IMes, IXy and their imidazolium salt precursors Synthetic routes to and diazadiene precursors for imidazolium salts. The imidazolium salt synthesis as a 1, 5-dipolar electrocyclization. Potential side-reactions in the imidazolium salt synthesis. Optimization of

Trapping evidence for the thermal cyclization of di-(o-acetylphenyl)acetylene to 3,3'-dimethyl- 1,1'-biisobenzofuran

• Charles P. Casey,
• Neil A. Strotman and
• Ilia A. Guzei

Beilstein J. Org. Chem. 2005, 1, No. 18, doi:10.1186/1860-5397-1-18

• phenylcarbenes to isobenzofurans. Ring opening of 2-furylcarbenes to alk-2-en-4-yn-1-ones. Coupled coarctate cyclization and 6π electrocyclization. Supporting Information Supporting Information File 26: bisfuran-supportinginfo.doc 100 Kb Acknowledgements Financial support from the National Science Foundation