Complete transfer of chirality in an intramolecular, thermal [2 + 2] cycloaddition of allene-ynes to form non-racemic spirooxindoles

• Kay M. Brummond and
• Joshua M. Osbourn

Beilstein J. Org. Chem. 2011, 7, 601–605, doi:10.3762/bjoc.7.70

• cyclobutene; allene; allenyloxindole; chiral lanthanide shift reagent; chiral transfer; Introduction The [2 + 2] cycloaddition reaction of allenes and alkynes provides rapid entry into synthetically challenging alkylidene cyclobutene ring systems. We, along with others, have demonstrated the intramolecular

Gold-catalyzed regioselective oxidation of terminal allenes: formation of α-methanesulfonyloxy methyl ketones

• Yingdong Luo,
• Guozhu Zhang,
• Erik S. Hwang,
• Thomas A. Wilcoxon and
• Liming Zhang

Beilstein J. Org. Chem. 2011, 7, 596–600, doi:10.3762/bjoc.7.69

• from terminal allenes in fair to good yields. The chemistry relies on a gold-catalyzed intermolecular oxidation of the 1,2-diene unit using 3,5-dichloropyridine N-oxide as the oxidant. The reaction tolerates a range of functional groups and shows excellent regioselectivity. Keywords: allene; catalysis

• ; gold; oxidation; regioselectivity; Introduction While alkynes are the most studied substrates in homogeneous gold catalysis [1][2][3][4][5][6][7][8][9], allenes [10] occupy a not-so-distant second place, and many versatile transformations have been developed either using allenes as substrates [11][12

• ][13][14][15][16][17] or via allenes generated in situ [18][19][20][21]. We have recently shown that highly reactive gold carbenes can be generated from alkynes via gold-promoted intermolecular oxidation by pyridine/quinoline N-oxides [22][23][24][25], making benign alkynes effective surrogates of

Synthesis of cross-conjugated trienes by rhodium-catalyzed dimerization of monosubstituted allenes

• Tomoya Miura,
• Tsuneaki Biyajima,
• Takeharu Toyoshima and
• Masahiro Murakami

Beilstein J. Org. Chem. 2011, 7, 578–581, doi:10.3762/bjoc.7.67

• Tomoya Miura Tsuneaki Biyajima Takeharu Toyoshima Masahiro Murakami Department of Synthetic Chemistry and Biological Chemistry, Kyoto University, Katsura, Kyoto 615-8510, Japan 10.3762/bjoc.7.67 Abstract A rhodium(I)/dppe catalyst promoted dimerization of monosubstituted allenes in a

• been developed. Among these, transition-metal-catalyzed dimerization of allenes presents a unique entry to substituted cross-conjugated trienes. For example, a nickel(0)/triphenylphosphine complex catalyzes a dimerization reaction of 3-methylbuta-1,2-diene to afford 2,5-dimethyl-3,4-bismethylenehex-1

• -ene [18][19]. The nickel-catalyzed reaction, however, leads to a complex mixture of products when monosubstituted allenes such as penta-1,2-diene and 1-phenylpropa-1,2-diene are employed [20]. On the other hand, a palladium-catalyzed dimerization reaction of monosubstituted allenes produces

Synthesis of chiral mono(N-heterocyclic carbene) palladium and gold complexes with a 1,1'-biphenyl scaffold and their applications in catalysis

• Lian-jun Liu,
• Feijun Wang,
• Wenfeng Wang,
• Mei-xin Zhao and
• Min Shi

Beilstein J. Org. Chem. 2011, 7, 555–564, doi:10.3762/bjoc.7.64

• NHC–Au(I) complex (S)-6a was consequently investigated as the catalyst in the asymmetric intramolecular hydroamination of allenes. This reaction has been achieved with high enantioselectivity by a chiral phosphine–Au(I) complex [87][88][89][90][91][92][93]. Treatment of allene 11 with (S)-6a and

Gold catalysis for organic synthesis

• F. Dean Toste

Beilstein J. Org. Chem. 2011, 7, 553–554, doi:10.3762/bjoc.7.63

• , cycloaddition and cycloisomerization reactions, to applications in enantioselective catalysis, oxidative coupling and the total synthesis of natural products, and transformations of alkynes, allenes, alkenes and even C–H bonds. A true treasure chest of reactivity! I am grateful to all of the authors that have

The arene–alkene photocycloaddition

• Ursula Streit and
• Christian G. Bochet

Beilstein J. Org. Chem. 2011, 7, 525–542, doi:10.3762/bjoc.7.61

• higher aromatics are more likely to undergo para cycloadditions [91], and that it is the main mode when allenes are involved [92]. A high yielding example of a para photocycloaddition with an allene has been published by Haddaway et al. (Scheme 30) [93]. If the irradiation is carried out in the presence

• benzoxepine by Jones et al. Photocycloaddition observed by Griesbeck et al. Mechanism proposed by Griesbeck et al. Intramolecular photocycloaddition of allenes to benzaldehydes.

Synthesis of 5-(2-methoxy-1-naphthyl)- and 5-[2-(methoxymethyl)-1-naphthyl]-11H-benzo[b]fluorene as 2,2'-disubstituted 1,1'-binaphthyls via benzannulated enyne–allenes

• Yu-Hsuan Wang,
• Joshua F. Bailey,
• Jeffrey L. Petersen and
• Kung K. Wang

Beilstein J. Org. Chem. 2011, 7, 496–502, doi:10.3762/bjoc.7.58

• synthesized by treatment of the corresponding benzannulated enediynes with potassium tert-butoxide in refluxing toluene to give benzannulated enyne–allenes for the subsequent Schmittel cascade cyclization reactions. The structures of these two 5-(1-naphthyl)-11H-benzo[b]fluorenes could be regarded as 2,2

• '-disubstituted 1,1'-binaphthyls with the newly constructed benzofluorenyl group serving as a naphthyl moiety. Keywords: benzannulated enediynyl alcohols; benzannulated enyne–allenes; 2,2'-disubstituted 1,1'-binaphthyls; 5-(1-naphthyl)-11H-benzo[b]fluorenes; Schmittel cascade cyclizations; Introduction

• Benzannulated enyne–allenes bearing an aryl substituent at the alkynyl terminus are excellent precursors of 5-aryl-11H-benzo[b]fluorenes [1][2][3][4][5]. Several synthetic pathways to the benzannulated enyne–allene systems have been reported, including generation in situ from the corresponding benzannulated

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

• possible involvement of the second set of allenic π-electrons. Nevertheless, the calculated ∆Eact value remains high at 77.7 kcal·mol−1 [2]. Whether concerted or not, most thermal isomerizations of allenes require severe reaction conditions (for general reviews on allenes see [3], for some examples of

• thermal isomerization of exocyclic allenes to dienes via radical intermediates see [4][5][6][7][8][9][10][11][12]), whereby controlling E/Z ratios of the resulting diene remains a difficult problem. On the other hand, a stepwise isomerization of allenes via acid-, base-, or metal-mediated conditions seem

• blocks, a number of stereoselective preparations are known. The major question here is how viable is it to access conjugated dienes from structurally more challenging allenes through a kinetically difficult and stereochemically undistinguished isomerization. It might not seem like a logical approach

Allene chemistry

• Kay M. Brummond

Beilstein J. Org. Chem. 2011, 7, 394–395, doi:10.3762/bjoc.7.50

• Kay M. Brummond University of Pittsburgh, Department of Chemistry, Chevron Science Center, 219 Parkman Avenue Pittsburgh, PA 15260, USA 10.3762/bjoc.7.50 Allenes: The changing landscape of Csp As organic chemists, we continually search for transformations to produce compounds in increasingly

• Organic Chemistry is allenes, which even after decades of use can still be classified as an underutilized functional group. However, great advances in the chemistry of allenes have been made since the time when they were thought to be, “difficult to prepare and very reactive, and not commonly encountered

• ...” [1]. I first became interested in allenes as a graduate student with Professor Ray Funk at Pennsylvania State University while working on the preparation of ene–diyne systems. Interestingly, I always seemed to isolate allenes instead of the compounds I was hoping to obtain. My interests in allenes

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

• spirocyclobutanes that are accessed via alkylation chemistry [5]. Alternatively, more structurally complex spirocyclobutanes have been obtained from homodimerization reactions of allenes or alkenes [6][7]. However, neither of these approaches provides an enabling strategy for accessing the densely functionalized

• ] cycloaddition reaction is that the reaction remains selective for the distal double bond of the allene even with densely functionalized allenes [29]. In addition, conversion of the propargylic acetate to the spirooxindole in one step provides a rapid and potentially stereoselective increase in molecular

A review of new developments in the Friedel–Crafts alkylation – From green chemistry to asymmetric catalysis

• Magnus Rueping and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2010, 6, No. 6, doi:10.3762/bjoc.6.6

• . Depending on the reaction conditions one observes either the corresponding dihydronaphthalenes or allenes as the main reaction products [92]. Catalytic propargylation of arenes (Prop-2-ynyl)arenes 84 are widely distributed structural motifs in organic chemistry due to the high synthetic value of the alkyne

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

• ][24]. In comparison, reported transformations for 3-bromo-benzopyrans and bromo-substituted naphthopyrans are still rare. One reason could be the well documented anionic cleavage of 3-bromo-substituted benzopyrans upon metal halogen exchange, resulting in the formation of allenes and subsequent

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

• Asuncion Barbero Francisco J. Pulido M. Carmen Sanudo Departamento de Química Orgánica, Universidad de Valladolid, 47011 Valladolid, Spain 10.1186/1860-5397-3-16 Abstract Addition of low order phenyldimethylsilylcyanocuprates to allenes followed by "in situ" reaction of the intermediate

• particular allylsilanes have attracted considerable attention due to the increasing number of new methodologies that allow useful synthetic transformations. [1][2] Over the last decade allenes have emerged as one of the best sources for the synthesis of allylsilanes. [3] Although unactivated allenes do not

• easily undergo organometallic addition – and do not react with carbocuprates – they are readily attacked by metallocuprates. [4] In particular, simple allenes react with silylcuprates and stannylcuprates giving rise to a great variety of allyl- and vinylsilanes and stannanes with different substitution

Synthesis of highly substituted allenylsilanes by alkylidenation of silylketenes

• Stephen P. Marsden and
• Pascal C. Ducept

Beilstein J. Org. Chem. 2005, 1, No. 5, doi:10.1186/1860-5397-1-5

• reaction, in line with our expectations, exemplified by the reactions of cyclohexyl-substituted ketene 1d (entries 7 and 8, compared with entries 1–6). In almost all cases, if reactions were left for extended periods beyond consumption of starting material, small quantities of desilylated allenes were