Synthesis of the B-seco limonoid core scaffold

• Hanna Bruss,
• Hannah Schuster,
• Rémi Martinez,
• Markus Kaiser,
• Andrey P. Antonchick and
• Herbert Waldmann

Beilstein J. Org. Chem. 2014, 10, 194–208, doi:10.3762/bjoc.10.15

• treatment did again lead to formation of enone 90. We assume that the additional substituents as well as the intermediary formed TMS ether cause excessive steric bulk and rigidity that prevent the silyl ketene acetals from adopting the required conformation. Hence, we considered enone 90 as an alternative

Synthesis of five- and six-membered cyclic organic peroxides: Key transformations into peroxide ring-retaining products

• Alexander O. Terent'ev,
• Dmitry A. Borisov,
• Vera A. Vil’ and
• Valery M. Dembitsky

Beilstein J. Org. Chem. 2014, 10, 34–114, doi:10.3762/bjoc.10.6

• hydroperoxy acetals 61a,b (Scheme 19) [250]. The ozonolysis of 9-methyleneheptadecane-7,11-diyl-bis(methanesulfonate) (63) gave 9-oxoheptadecane-7,11-diyl-bis(methanesulfonate) (64). The latter reacted with H2O2 in the presence of sulfuric acid (or iodine) as the catalyst to form 9,9-dihydroperoxyheptadecane

• the hydroperoxy acetals 229 under basic conditions. This method is suitable for the efficient synthesis of functionalized 1,2-dioxanes 230 in moderate to high yields (Scheme 65, Table 17). In early studies, scandium(III) triflate was used as the catalyst for the hydroperoxidation of ketones with the

New developments in gold-catalyzed manipulation of inactivated alkenes

• Michel Chiarucci and
• Marco Bandini

Beilstein J. Org. Chem. 2013, 9, 2586–2614, doi:10.3762/bjoc.9.294

• enabled the use of simple dimethyl acetals 6 in the carboalkoxylation of alkenes (Scheme 4) [32]. A 1:2 mixture of [picAuCl2] (7) and AgNTf2 efficiently catalyzed the double functionalization of aryl alkenes 4 in good yields and mild conditions. Dialkyl substituted olefins afforded the product only in

• moderate yields whereas monoalkyl olefins were completely unreactive under the optimized conditions. Although an activation of the acetals by the gold catalyst cannot be ruled out, a reaction pathway involving gold activation of the alkene, followed by addition of the alkyl gold intermediate 10 to the

• )]-catalyzed addition of aliphatic alcohols to alkenes. [Au(III)]-catalyzed carboalkoxylation of alkenes with dimethyl acetals 6. Isolation and reactivity of alkyl gold intermediates in the intramolecular hydroamination of alkenes. [Au(I)]-catalyzed intermolecular hydroamination of dienes. Intramolecular [Au(I

Synthesis of mucin-type O-glycan probes as aminopropyl glycosides

• David Benito-Alifonso,
• Rachel A. Jones,
• Anh-Tuan Tran,
• Hannah Woodward,
• Nichola Smith and
• M. Carmen Galan

Beilstein J. Org. Chem. 2013, 9, 1867–1872, doi:10.3762/bjoc.9.218

• cleavage of the 4,6-O-benzylidene acetals using p-TsOH in MeOH under sonication followed by removal of the N-Troc groups in the presence of LiOH and subsequent acetylation with pyridine and acetic anhydride formed the desired acetamido functionalities, removal of the ester groups under basic conditions was

Gold-catalyzed cyclization of allenyl acetal derivatives

• Dhananjayan Vasu,
• Samir Kundlik Pawar and
• Rai-Shung Liu

Beilstein J. Org. Chem. 2013, 9, 1751–1756, doi:10.3762/bjoc.9.202

• Dhananjayan Vasu Samir Kundlik Pawar Rai-Shung Liu Department of Chemistry, National Tsing Hua University, Hsinchu, 30013, Taiwan (ROC) 10.3762/bjoc.9.202 Abstract The gold-catalyzed transformation of allenyl acetals into 5-alkylidenecyclopent-2-en-1-ones is described. The outcome of our

• of the acetate group at the allyl cation intermediate. Keywords: allenyl acetals; 5-alkylidenecyclopent-2-en-1-ones; cyclization; gold catalysis; Introduction Gold-catalyzed cyclization/cycloaddition reactions [1][2][3][4][5] are useful synthetic methods to construct complicated carbo- and

• oxacyclic frameworks. Such cascade reactions have been well studied on various difunctionalized molecules including oxoalkynes [6][7][8][9][10][11][12][13], oxoallenes [14], oxoalkenes [15] and allenyl acetals [16][17][18]. In this cascade sequence, two new rings and three chemical bonds are generated in a

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

• a Brønsted acid. Keywords: allylation; hemiacetal; O,O-acetal; O,S-thioacetal; peroxyacetal; Re2O7; S,S-acetal; Introduction The synthetically important conversions of hemiacetals to acetals, thioacetals, or homoallyl ethers are typically achieved through activation of the substrate with a strong

• , tetrahydropyranol 4a and the O-t-butyldimethylsilyl ether of the latter (4b). While good yields of acetals were obtained from the reaction with primary or secondary alcohols, or t-butyl hydroperoxide, acetalization with phenol proceeded in poor yield. Attempted acetalizations of 2,3,4,6-tetrabenzylglucose, the

• nucleophiles Perrhenate proved ineffective for catalyzing the formation of N,O-acetals (Table 6). Although these investigations were complicated by the limited solubility of some of the nucleophiles in dichloromethane, similar results were obtained in acetonitrile, where solubility was less of an issue. The

Diastereoselective synthesis of nitroso acetals from (S,E)-γ-aminated nitroalkenes via multicomponent [4 + 2]/[3 + 2] cycloadditions promoted by LiCl or LiClO₄

• Leandro Lara de Carvalho,
• Robert Alan Burrow and
• Vera Lúcia Patrocinio Pereira

Beilstein J. Org. Chem. 2013, 9, 838–845, doi:10.3762/bjoc.9.96

• Materiais Inorgânicos, Universidade Federal de Santa Maria, 97105-900, Santa Maria, Rio Grande do Sul, RS, Brazil 10.3762/bjoc.9.96 Abstract Chiral nonracemic aminated nitroso acetals were synthesized via diastereoselective multicomponent [4 + 2]/[3 + 2] cycloadditions employing new (S,E)-γ-nitrogenated

• nitroalkenes 5a–c as heterodienes, ethyl vinyl ether (EVE) as a dienophile, and selected electron-deficient alkenes as 1,3-dipolarophiles. The employment of different organic solutions of LiClO4 or LiCl as promoter systems provided the respective nitroso acetals with yields from 34–72% and good levels of

• -dipolarophiles to furnish nitroso acetals of type 4 in an inter- or intramolecular fashion [1][2][3][8][9]. These nitroso acetals can be transformed into functionalized pyrrolizidin-3-ones and in sequence into alkaloid nuclei [1][3][10][11]. The majority of the tandem nitroalkene cycloadditions require the

Spectroscopic characterization of photoaccumulated radical anions: a litmus test to evaluate the efficiency of photoinduced electron transfer (PET) processes

• Maurizio Fagnoni,
• Stefano Protti,
• Davide Ravelli and
• Angelo Albini

Beilstein J. Org. Chem. 2013, 9, 800–808, doi:10.3762/bjoc.9.91

• ], aliphatic acetals and ketals [16], ethers [17], organostannanes [18][19], organosilanes [20][21][22], aromatics [10][23][24], and even alkanes [25][26][27]. BET (path a') could ensue, thus leading to no chemical change. However, when the D–X•+ intermediate contained a good electrofugal group (such as a

Inter- and intramolecular enantioselective carbolithiation reactions

• Asier Gómez-SanJuan,
• Nuria Sotomayor and
• Esther Lete

Beilstein J. Org. Chem. 2013, 9, 313–322, doi:10.3762/bjoc.9.36

• stabilized by coordination with a Lewis-basic substituent, react with different electrophiles in a highly diastereoselective manner. On the other hand, when acetals derived from cinnamyl alcohols are used as substrates, cyclopropanes 6 can be obtained in high enantiomeric excess by warming the reaction

Removal of benzylidene acetal and benzyl ether in carbohydrate derivatives using triethylsilane and Pd/C

• Abhishek Santra,
• Tamashree Ghosh and
• Anup Kumar Misra

Beilstein J. Org. Chem. 2013, 9, 74–78, doi:10.3762/bjoc.9.9

• Abhishek Santra Tamashree Ghosh Anup Kumar Misra Bose Institute, Division of Molecular Medicine, P-1/12, C.I.T. Scheme VII-M, Kolkata-700054, India; FAX: 91-33-2355 3886 10.3762/bjoc.9.9 Abstract Clean deprotection of carbohydrate derivatives containing benzylidene acetals and benzyl ethers was

• reported for the removal of benzylidene acetals by using strong protic and Lewis acids [10][11][15] as well as some heterogeneous acidic catalysts [16][17]. Removal of benzylidene acetal under nonacidic conditions includes hydrogenolysis using hydrogen gas over Pd/C [18], or treatment with hydrazine [19

• development of a mild, neutral reaction condition for the removal of benzylidene acetals would be useful in the derivatization of a carbohydrate framework. Mandal et al. reported the removal of benzyl esters/ethers and the reduction of alkenes/alkynes by catalytic transfer hydrogenation using a combination

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

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

A Wittig-olefination–Claisen-rearrangement approach to the 3-methylquinoline-4-carbaldehyde synthesis

• Mukund G. Kulkarni,
• Mayur P. Desai,
• Deekshaputra R. Birhade,
• Yunus B. Shaikh,
• Ajit N. Dhatrak and
• Ramesh Gannimani

Beilstein J. Org. Chem. 2012, 8, 1725–1729, doi:10.3762/bjoc.8.197

• underwent Claisen rearrangement to give 4-pentenals 3a–h. Protection of the aldehyde group of the 4-pentenals as acetals 4a–h and subsequent oxidative cleavage of the terminal olefin furnished nitroaldehydes 5a–h. Reductive cyclization of these nitroaldehydes yielded the required 3-methylquinoline-4

• with ethylene glycol furnished the corresponding acetals 4a–h in good yields (Table 1). From the NMR spectra of these acetals, it was clear that they were also a mixture of diastereomers, although they appeared to be homogeneous on TLC. All attempts to separate the diastereomers at this stage were also

• unsuccessful. Subjecting these acetals to oxidative cleavage in aq THF furnished the aldehydes 5a–h in good yields (Table 1). The NMR of these aldehydes revealed them again to be a mixture of diastereomers, although they appeared to be homogeneous on TLC. Reductive cyclization of these nitroaldehydes furnished

Synthesis of 5-oxyquinoline derivatives for reversal of multidrug resistance

• Torsten Dittrich,
• Nils Hanekop,
• Nacera Infed,
• Lutz Schmitt and
• Manfred Braun

Beilstein J. Org. Chem. 2012, 8, 1700–1704, doi:10.3762/bjoc.8.193

• better for Pdr5. Keywords: acetals; enantiopure compounds; heterocycles; inhibitor; multidrug resistance; Introduction The treatment of cancer is often severely hampered by efflux pumps, which are responsible for the extrusion of various chemotherapeutics from the tumor cell, an effect termed

• of the stereogenic carbinol center. Thus, we replaced the piperazine motif in 1 by a piperidine ring carrying either nitrogen or oxygen as a hetero substituent(s) in the 4-position. Therefore, an initial series of 4-aminopiperidines 2a–4a and, in a second approach, new spirocyclic acetals 5a–12a as

• well as the thioacetal 13a were synthesized. All the new compounds, shown in Scheme 1, were obtained in enantiomerically pure form, with the stereogenic carbinol center adopting (R) configuration. The acetals 8a and 9a formed as mixtures of diastereomers, whereas compound 10a was enantiomerically and

The Amadori rearrangement as glycoconjugation method: Synthesis of non-natural C-glycosyl type glycoconjugates

• Katharina Gallas,
• Gerit Pototschnig,
• Florian Adanitsch,
• Arnold E. Stütz and
• Tanja M. Wrodnigg

Beilstein J. Org. Chem. 2012, 8, 1619–1629, doi:10.3762/bjoc.8.185

• corresponding acetals when the pH value is kept below 6 [30]. In the D-gluco series, D-glycero-D-gulo-aldoheptose 10 was isolated in 81% yield, and no C-2 epimer was detected, as shown by comparison of the NMR data with a commercial sample [31]. Aldoheptose 10 was taken to the Amadori rearrangement without

Organocatalytic C–H activation reactions

• Subhas Chandra Pan

Beilstein J. Org. Chem. 2012, 8, 1374–1384, doi:10.3762/bjoc.8.159

• , ether and acetals delivering the products 7 in good to excellent yields (50–94%). The reaction was also compatible with different ketones although extended reaction times were required to obtain good yields of the desired products. Interestingly, when the substrates were extended to five and six

Synthesis of fluorinated maltose derivatives for monitoring protein interaction by ¹⁹F NMR

• Michaela Braitsch,
• Hanspeter Kählig,
• Georg Kontaxis,
• Michael Fischer,
• Toshinari Kawada,
• Robert Konrat and
• Walther Schmid

Beilstein J. Org. Chem. 2012, 8, 448–455, doi:10.3762/bjoc.8.51

• regioselective reductive ring opening of benzylidene acetals in the maltose derivative 11 was performed with a complex of BH3/Bu2BOTf at −70 °C [32][33]. Fluorination with DAST [34][35] was performed in a sealed tube for 1 h at 80 °C under microwave conditions. The deprotection of the benzyl group was achieved

Acceptor-influenced and donor-tuned base-promoted glycosylation

• Stephan Boettcher,
• Martin Matwiejuk and
• Joachim Thiem

Beilstein J. Org. Chem. 2012, 8, 413–420, doi:10.3762/bjoc.8.46

• yields of up to 95%. Preparation of the 3-O-monobenzylated methyl α- and β-D-galactopyranosyl acceptors 5 and 6 was achieved via stannylidene acetals [6] (Scheme 2). Compound 18 was subjected to a one-step synthesis with Bu2SnO and BnBr, affording target compound 5. The synthetic route for the methyl β

Recent advances in the gold-catalyzed additions to C–C multiple bonds

• He Huang,
• Yu Zhou and
• Hong Liu

Beilstein J. Org. Chem. 2011, 7, 897–936, doi:10.3762/bjoc.7.103

• benzobicyclo[5.3.1]acetals 87 were produced when triazole–gold was employed as the catalyst. With alcohol nucleophiles, gold(I)-catalyzed cyclization of o-alkynyl benzaldehyde 88 and benzaldimine–chromium complexes gave stereoselectively 1-anti-functionalized heterocycle chromium complexes 89 (Scheme 16) [47

Synthesis of novel 5-alkyl/aryl/heteroaryl substituted diethyl 3,4-dihydro-2H-pyrrole-4,4-dicarboxylates by aziridine ring expansion of 2-[(aziridin-1-yl)-1-alkyl/aryl/heteroaryl-methylene]malonic acid diethyl esters

• Satish S. More,
• T. Krishna Mohan,
• Y. Sateesh Kumar,
• U. K. Syam Kumar and
• Navin B. Patel

Beilstein J. Org. Chem. 2011, 7, 831–838, doi:10.3762/bjoc.7.95

• reactions led to various by-products probably as a result of protonation and dehydrohalogenation of the presumed intermediates [28] (Scheme 1). Junjappa and co-workers were successful in iodide ion mediated ring expansion of N-vinylaziridine N,S-acetals containing cyano- and ester groups on the β-carbon and

When cyclopropenes meet gold catalysts

• Frédéric Miege,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2011, 7, 717–734, doi:10.3762/bjoc.7.82

• determination of the cationic or carbenic nature of organogold intermediates, but the presence of the two oxygen atoms in cyclopropenone acetals unavoidably led to more favorable cationic forms and hence cannot provide a general answer. Using the M06 functional of DFT, Toste et al. calculated rotational

• by ring-opening of 3 should instead react as a gold-stabilized carbocation due to the presence of oxygen atoms that can stabilize the cationic intermediate. However, it is worth pointing out that Boger and Brotherton previously reported that cyclopropenone acetals could cyclopropanate electron

• new possibilities and further synthetic developments in this field will certainly be reported. General reactivity of cyclopropenes in the presence of gold catalysts. Cationic organogold species generated from cyclopropenone acetals. Rotation barriers around the C2–C3 bond (M06 DFT calculations). Au–C1

Synthesis, reactivity and biological activity of 5-alkoxymethyluracil analogues

• Lucie Brulikova and
• Jan Hlavac

Beilstein J. Org. Chem. 2011, 7, 678–698, doi:10.3762/bjoc.7.80

• )pyrimidines 68 and 69. The latter readily underwent nucleophilic attack by alkoxide ions to yield alicyclic or cyclic acetals 70–73 and 74, respectively, depending on the alcohol used. Uridine and arabinofuranosyl analogues: 5-Substituted uracil nucleosides where the sugar component is ribose or arabinose

Gold-catalyzed heterocyclizations in alkynyl- and allenyl-β-lactams

• Benito Alcaide and
• Pedro Almendros

Beilstein J. Org. Chem. 2011, 7, 622–630, doi:10.3762/bjoc.7.73

• . Deauration and proton transfer leads to adduct 27 with concomitant regeneration of the Au(III) species (Scheme 15). Regiocontrolled gold/Brønsted acid co-catalyzed direct bis-heterocyclization of alkynyl-β-lactams allows the efficient synthesis of optically pure tricyclic bridged acetals bearing a 2

• . Possible catalytic cycle for the gold-catalyzed cyclization of MOM protected alkynol derivatives. Gold/Brønsted acid co-catalyzed formation of bridged β-lactam acetals from 2-azetidinone-tethered alkynyl dioxolanes. Acknowledgements Support for this work by the MICINN (Project CTQ2009-09318), Comunidad

Synthesis of glycoconjugate fragments of mycobacterial phosphatidylinositol mannosides and lipomannan

• Benjamin Cao,
• Jonathan M. White and
• Spencer J. Williams

Beilstein J. Org. Chem. 2011, 7, 369–377, doi:10.3762/bjoc.7.47

• reductively-removed protecting groups such as benzyl ethers must be avoided owing to their incompatibility with the azido group when using H2/Pd or Na/NH3. We therefore sought to develop a synthesis based on the use of esters, silyl ethers and acetals only. Synthesis of monosaccharide building blocks

Approaches towards the synthesis of 5-aminopyrazoles

• Ranjana Aggarwal,
• Vinod Kumar,
• Rajiv Kumar and
• Shiv P. Singh

Beilstein J. Org. Chem. 2011, 7, 179–197, doi:10.3762/bjoc.7.25

• corresponding 5-amino-3-arylamino-1-phenylpyrazole-4-carboxamides 90 (Scheme 25) [67]. Ketene S,S- and S,N-acetals or tetracyanoethylene 91 on reaction with 3-hydrazino-6-(p-tolyl)pyridazine afforded the 5-amino-4-cyanopyrazoles 92 (Scheme 26) [68]. Several thiazolylpyrazoles 97–100 bearing a variety of

Heavy atom effects in the Paternò–Büchi reaction of pyrimidine derivatives with 4,4’-disubstituted benzophenones

• Feng-Feng Kong,
• Jian-Bo Wang and
• Qin-Hua Song

Beilstein J. Org. Chem. 2011, 7, 113–118, doi:10.3762/bjoc.7.16

• Paternò–Büchi reaction, spin-transition processes would be affected, and this may lead to interesting results. Abe et al. [14] investigated the effect of a sulfur atom on the stereoselective formation of oxetanes in Paternò–Büchi reaction of aromatic aldehydes with silyl O,S-ketene acetals to give trans-3