C–C (alkynylation) vs C–O (ether) bond formation under Pd/C–Cu catalysis: synthesis and pharmacological evaluation of 4-alkynylthieno[2,3-d]pyrimidines

• Dhilli Rao Gorja,
• K. Shiva Kumar,
• K. Mukkanti and
• Manojit Pal

Beilstein J. Org. Chem. 2011, 7, 338–345, doi:10.3762/bjoc.7.44

• potential inhibition of TS [15]. The CMe2OH group next to the alkynyl moiety may facilitate the binding of the TS enzyme through its sulfhydryl (–SH) moiety with compounds 3f and 3g thereby generating the corresponding drug–enzyme allene intermediates (Figure 2). Nevertheless, the present study indicated

A thermally-induced, tandem [3,3]-sigmatropic rearrangement/[2 + 2] cycloaddition approach to carbocyclic spirooxindoles

• Kay M. Brummond and
• Joshua M. Osbourn

Beilstein J. Org. Chem. 2010, 6, No. 33, doi:10.3762/bjoc.6.33

• -2-one and an alkyne. The cycloaddition reaction occurs selectively with the distal double bond of the allene, is tolerant of a phenyl and trimethylsilyl group on the terminus of the alkyne, and can be used to access bicyclo[4.2.0]octadienes and bicyclo[5.2.0]nonadienes. The allene precursors are not

• observed, but are likely intermediates of an infrequently encountered thermal [3,3]-sigmatropic rearrangement of a propargylic acetate. Keywords: allene; propargylic acetate; spirooxindole; thermal [2 + 2] cycloaddition; thermal [3,3]-sigmatropic rearrangement; vinylidene indolin-2-one; Introduction

• discovery of new biological probes and pharmaceuticals [8]. We recently disclosed a thermal [2 + 2] cycloaddition reaction of allene-ynes to provide a variety of alkylidene cyclobutenes in good yields [9][10][11][12][13][14][15][16][17][18]. Notable features of this reaction were the stability of the

Synthesis of novel photochromic pyrans via palladium- mediated reactions

• Christoph Böttcher,
• Gehad Zeyat,
• Saleh A. Ahmed,
• Elisabeth Irran,
• Thorben Cordes,
• Cord Elsner,
• Wolfgang Zinth and
• Karola Rueck-Braun

Beilstein J. Org. Chem. 2009, 5, No. 25, doi:10.3762/bjoc.5.25

• ). Typically the thermal reversion of the open forms is very fast [17][18][19][20]. Quite recently, the formation of allene intermediates at low temperatures was also reported in the literature. They originate from open merocyanine isomers and are formed via a 1,5-hydrogen shift reaction [21][22]. However

• , these allene intermediates can be avoided by the replacement of hydrogen in the immediate vicinity of the two aryl residues (3-position of 2H-1-benzopyrans and 2-position of 3H-naphtho[2,1-b]pyrans). Thereby, the photochromism of benzo- and naphthopyrans is expected to be simplified for biological

Allylsilanes in the synthesis of three to seven membered rings: the silylcuprate strategy

• Asunción Barbero,
• Francisco J. Pulido and
• M. Carmen Sañudo

Beilstein J. Org. Chem. 2007, 3, No. 16, doi:10.1186/1860-5397-3-16

• key step is the syn addition of the tin cuprate to the acetylene, which controls the cis stereochemistry required for cyclization. [23] Seven Membered Carbocycles The use of nitriles and imines as electrophiles in the silylcupration of allene provides new alternatives for carbocyclization. Recently

• , we showed that α,β-unsaturated nitriles undergo a double addition process when treated with the cuprate species resulting from addition of 1 to allene, giving ketones 44 containing both an allylsilane group and a vinylsilane moiety (Scheme 10). [24] Equilibration between species 2 and 45 as the

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

• oxygen on the near carbon of the alkyne produces intermediate B (Scheme 7). This attack might be catalyzed by protonation of a carbonyl by adventitious acid. The enolate (or enol) oxygen of B would then attack the central carbon of the allene, closing the second ring and forming biisobenzofuran A. In a