Re₂O₇-catalyzed reaction of hemiacetals and aldehydes with O-, S-, and C-nucleophiles

• Wantanee Sittiwong,
• Michael W. Richardson,
• Charles E. Schiaffo,
• Thomas J. Fisher and
• Patrick H. Dussault

Beilstein J. Org. Chem. 2013, 9, 1526–1532, doi:10.3762/bjoc.9.174

• Brønsted or Lewis acid, or by conversion to an activated intermediate such as a haloacetal [1]. Perrhenates, best known as catalysts for large-scale alkene metathesis [2] and isomerization of allylic alcohols [3][4][5][6][7][8][9][10], have been shown to promote condensation of carbonyls with hydrogen

Copper(II)-salt-promoted oxidative ring-opening reactions of bicyclic cyclopropanol derivatives via radical pathways

• Eietsu Hasegawa,
• Minami Tateyama,
• Ryosuke Nagumo,
• Eiji Tayama and
• Hajime Iwamoto

Beilstein J. Org. Chem. 2013, 9, 1397–1406, doi:10.3762/bjoc.9.156

• interconverting 9 and 10 through 8 [22][23][24][25][26][27][28][29][30] might occur (see below). A mechanism on the fragmentation of initially formed metal–organic complexes, giving β-ketoalkyl radicals [40], cyclopropoxy radicals [25][28][48][49][50], or β-metalated carbonyls [39], is still controversial [35][36

Lanostane- and cycloartane-type triterpenoids from Abies balsamea oleoresin

• Serge Lavoie,
• Charles Gauthier,
• Jean Legault,
• Sylvain Mercier,
• Vakhtang Mshvildadze and
• André Pichette

Beilstein J. Org. Chem. 2013, 9, 1333–1339, doi:10.3762/bjoc.9.150

• quaternary carbons, including those at δC 170.8 and 207.6 representing carboxylic and ketone carbonyls, respectively (Table 1). The 1H NMR spectrum showed two doublets at δH 0.35 (J = 3.9 Hz) and 0.52 (J = 3.9 Hz) characteristic of a cyclopropane ring (Table 2), suggesting that 4 is a member of the

Features of the behavior of 4-amino-5-carboxamido-1,2,3-triazole in multicomponent heterocyclizations with carbonyl compounds

• Eugene S. Gladkov,
• Katerina A. Gura,
• Svetlana M. Sirko,
• Sergey M. Desenko,
• Ulrich Groth and
• Valentin A. Chebanov

Beilstein J. Org. Chem. 2012, 8, 2100–2105, doi:10.3762/bjoc.8.236

• involving aminazoles, carbonyls and active methylene compounds can be effectively controlled by variation of such reaction parameters as temperature, solvent type, catalytic system, method of activation, etc. [9][10][11][12][13][14][15][16][17]. Changing these parameters gives us the opportunity to

• , carbonyls and active methylene compounds. In the present article we disclose our recent results of a study of such MCRs and analyze the influence of some of the reaction parameters on their development and outcome. Results and Discussion It was found that reaction between one equivalent of aminotriazole 1

Metal–ligand multiple bonds as frustrated Lewis pairs for C–H functionalization

• Matthew T. Whited

Beilstein J. Org. Chem. 2012, 8, 1554–1563, doi:10.3762/bjoc.8.177

• those explored more recently for main-group FLPs. The first type of reaction exhibited by M═E FLPs containing π-basic ligands is with polar multiple bonds such as carbonyls. The nucleophilic multiply bonded group can attack the electrophilic carbon atom, ultimately leading to metallacycle formation and

Two-directional synthesis as a tool for diversity-oriented synthesis: Synthesis of alkaloid scaffolds

• Kieron M. G. O’Connell,
• Monica Díaz-Gavilán,
• Warren R. J. D. Galloway and
• David R. Spring

Beilstein J. Org. Chem. 2012, 8, 850–860, doi:10.3762/bjoc.8.95

• Lewis acid molecules simultaneously. If the Dieckmann reaction occurs via a standard 6-membered transition state, it requires both carbonyls to be either coordinated to, or bonded to, a single metal centre, and so this could go some way towards explaining the apparent course of the reaction. Assuming

• occur via a chelated transition state such as 12, in which both carbonyls are coordinated to a single metal centre. The data in Table 1 provides further support for the suggestion that different mechanisms can operate depending on the amount of Lewis acid used. This support is provided by the fact that

Alkoxide-induced ring opening of bicyclic 2-vinylcyclobutanones: A convenient synthesis of 2-vinyl-substituted 3-cycloalkene-1-carboxylic acid esters

• Xiufang Ji,
• Zhiming Li,
• Quanrui Wang and
• Andreas Goeke

Beilstein J. Org. Chem. 2012, 8, 650–657, doi:10.3762/bjoc.8.72

• derivatives. Frequently employed ones include the thermal [2 + 2] cycloaddition of ketenes to alkenes and the polar addition of cyclopropyl ylides to carbonyls [1][2]. These methods generally allow regioselective as well as stereoselective syntheses of extensively substituted four-membered ring carbocycles

A straightforward approach towards combined α-amino and α-hydroxy acids based on Passerini reactions

• Ameer F. Zahoor,
• Sarah Thies and
• Uli Kazmaier

Beilstein J. Org. Chem. 2011, 7, 1299–1303, doi:10.3762/bjoc.7.151

• isonitrile-based MCRs (IMCR) especially have developed exceptionally well during the last few decades [7][8]. Based on the pioneering work of Passerini, who observed the first three-component coupling of carbonyls with carboxylic acids and isonitriles in 1921 [9], the so-called Passerini reaction became a

Recent developments in gold-catalyzed cycloaddition reactions

• Fernando López and
• José L. Mascareñas

Beilstein J. Org. Chem. 2011, 7, 1075–1094, doi:10.3762/bjoc.7.124

• (VIII) that participate in (4 + 2) annulations with polarized alkenes such as indoles, carbonyls, imines or silyl enol ethers [45]. Thus, different types of 6-membered carbocycles and heterocycles were prepared in good yields and notable regioselectivities. An example of these annulations, using indoles

Construction of cyclic enones via gold-catalyzed oxygen transfer reactions

• Leping Liu,
• Bo Xu and
• Gerald B. Hammond

Beilstein J. Org. Chem. 2011, 7, 606–614, doi:10.3762/bjoc.7.71

• labeling experiment was designed to elucidate the pathway responsible for the gold-catalyzed intramolecular oxygen transfer of 2-alkynyl-1,5-diketones (Scheme 8). By introducing an 18O atom into one of the carbonyls of the substrate, and using the 13C NMR spectra of the substrate and product to locate the

Formation of macrocyclic lactones in the Paternò–Büchi dimerization reaction

• Junya Arimura,
• Tsutomu Mizuta,
• Yoshikazu Hiraga and
• Manabu Abe

Beilstein J. Org. Chem. 2011, 7, 265–269, doi:10.3762/bjoc.7.35

• : furans; macrocyclic lactone; oxetane; Paternò–Büchi reaction; photochemical reaction; Findings Photochemical [2 + 2] cycloaddition reaction of alkenes with carbonyls, so-called Paternò–Büchi reaction [1][2][3][4][5][6][7][8][9][10][11][12][13], is one of the most efficient methods for preparing

• 359.07391. X-ray crystal structure of the macrocyclic lactone 2a. 1H NMR spectra (500 MHz) for (a) the photolysate of 1a after 4 h irradiation in degassed and dried C6D6 solution, (b) for isolated macrocyclic lactone 2a, and (c) for furan-2-carbaldehyde (3). Reaction of furan with triplet excited carbonyls

Chain stopper engineering for hydrogen bonded supramolecular polymers

• Thomas Pinault,
• Bruno Andrioletti and
• Laurent Bouteiller

Beilstein J. Org. Chem. 2010, 6, 869–875, doi:10.3762/bjoc.6.102

• [33]. The rigidity of the cyclic ureas forbids any conformational rearrangement and should make it possible to probe whether the presence of NH functions in S1 significantly affects the chain stopper efficiency. In order to see if both urea carbonyls in S2 interact cooperatively with EHUT assemblies

• participate in hydrogen bonding and reduce the efficiency of the stopper. Secondly, the lower viscosity of solutions containing S2 than those containing S3 indicates that both carbonyls are probably involved in the association between S2 and an EHUT filament. Finally, bis-thiourea S4 is a reasonably good

Molecular recognition of organic ammonium ions in solution using synthetic receptors

• Andreas Späth and
• Burkhard König

Beilstein J. Org. Chem. 2010, 6, No. 32, doi:10.3762/bjoc.6.32

Gold film- catalysed benzannulation by Microwave- Assisted, Continuous Flow Organic Synthesis (MACOS)

• Gjergji Shore,
• Michael Tsimerman and
• Michael G. Organ

Beilstein J. Org. Chem. 2009, 5, No. 35, doi:10.3762/bjoc.5.35

• exploring complex, multi-step catalytic processes in flow. The benzannulation reaction between aromatic carbonyls and alkynes has received increasing attention since 2002 [29][30]. This transformation has been shown to be promoted by Lewis acids, copper complexes [31] and various gold species, including Au

• , 124.6, 122.2, 51.0, 45.7, 20.4. HRMS calcd. for C29H28N2O2: 436.2151; found 436.2147. Mechanism of Au(III)-catalyzed benzannulation between aromatic carbonyls and alkynes. X-ray analysis of the metal films used in this benzannulation study. Panels a–e are scanning-electron micrographs (SEM) of all films

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

Beilstein J. Org. Chem. 2009, 5, No. 33, doi:10.3762/bjoc.5.33

• compound 40 are conjugated with the ketone through the aromatic ring. Thus, the lactam behaves as an imide whose carbonyls express ketone-like reactivity. Moreover, the upper carbonyl is deactivated by conjugation with a methoxy group in the ortho position of the benzene ring, and by the steric crowding by

One-pot preparation of substituted pyrroles from α-diazocarbonyl compounds

• Fernando de C. da Silva,
• Mauricio G. Fonseca,
• Renata de S. Rianelli,
• Anna C. Cunha,
• Maria C. B. V. de Souza and
• Vitor F. Ferreira

Beilstein J. Org. Chem. 2008, 4, No. 45, doi:10.3762/bjoc.4.45

• and 6 was observed since the former reaction involves a nucleophilic attack to vinylogous carbonyls of 3-carbonyl-dihydrofurans. In general, the yields were dependent basically on the reactivity of the diazocompounds. In fact, diazocompound 3 led to higher yields and lower reaction times than 1 or 2

Diels- Alder reactions using 4,7-dioxygenated indanones as dienophiles for regioselective construction of oxygenated 2,3-dihydrobenz[f]indenone skeleton

• Natsuno Etomi,
• Takuya Kumamoto,
• Waka Nakanishi and
• Tsutomu Ishikawa

Beilstein J. Org. Chem. 2008, 4, No. 15, doi:10.3762/bjoc.4.15

• molecular orbitals of quinone 8 supported this proposal, in which a larger LUMO coefficient (0.295) was obtained at C6 compared with C5 (0.244, Figure 5a). On the other hand, the reverse of the selectivity was expected when Lewis acid is coordinated with two carbonyls at C1 and C7 to positively activate the

The use of silicon- based tethers for the Pauson- Khand reaction

• Adrian P. Dobbs,
• Ian J. Miller and
• Saša Martinović

Beilstein J. Org. Chem. 2007, 3, No. 21, doi:10.1186/1860-5397-3-21

• not coming together, substituents were introduced to the tether chains, in an attempt to produce a Thorpe-Ingold-type effect and force the two ends of the chain together (Figure 2). There now exist a plethora both of alternative metal carbonyls and promoters for the Pauson Khand reaction. Using each

• each compound were first prepared and characterised, prior to addition of the promoter. Unfortunately, none of the promoters gave any of the desired products but simply de-complexed starting materials were recovered in each case. Alternative metal carbonyls were also investigated, with compounds 1–4

The vicinal difluoro motif: The synthesis and conformation of erythro- and threo- diastereoisomers of 1,2-difluorodiphenylethanes, 2,3-difluorosuccinic acids and their derivatives

• David O'Hagan,
• Henry S. Rzepa,
• Martin Schüler and
• Alexandra M. Z. Slawin

Beilstein J. Org. Chem. 2006, 2, No. 19, doi:10.1186/1860-5397-2-19

• conformation as it is typical for this functional group (Figure 10) with the C-F bonds only 23° off the plane. The carbonyls point in opposite directions and thus intramolecular hydrogen bonding is not possible. There is however strong intermolecular hydrogen bonding between the amide hydrogen and the carbonyl

A convenient synthesis of γ-functionalized cyclopentenones

• Nour Lahmar,
• Taïcir Ben Ayed,
• Moncef Bellassoued and
• Hassen Amri

Beilstein J. Org. Chem. 2005, 1, No. 11, doi:10.1186/1860-5397-1-11

• converted into other useful groups such as amines or carbonyls.[13][14] Treatment of α,β-unsaturated ketones 1[15] with primary nitroalkanes was achieved by refluxing the mixture at 50°C in THF using sodium methoxide as base (Scheme 1), resulting in full conversion and yielding the Michael adducts 2 (Table

• carbonyls by the formation of the nitronate anion in the presence of sodium methoxide followed by its addition to concentrated sulfuric acid at -50°C, allowed the formation of the 1,4-diketones 3 in fair to good yields (Table 1). During recent years, some cyclopentenones derivatives were known to exhibit

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

• carbenoid-based reagents. Introduction Allenylsilanes are versatile intermediates for organic synthesis.[1][2] They have two main modes of reactivity: firstly, as propargyl anion equivalents in thermal [3][4] or Lewis acid-mediated [5][6] addition to carbonyls, acetals and imines, and secondly as three