Homogeneous and heterogeneous photoredox-catalyzed hydroxymethylation of ketones and keto esters: catalyst screening, chemoselectivity and dilution effects

• Axel G. Griesbeck and
• Melissa Reckenthäler

Beilstein J. Org. Chem. 2014, 10, 1143–1150, doi:10.3762/bjoc.10.114

• -catalyzed photohydroxymethylation of ketones by methanol were investigated in order to evaluate the most active photocatalyst system. Dialkoxytitanium dichlorides are the most efficient species for chemoselective hydroxymethylation of acetophenone as well as other aromatic and aliphatic ketones. Pinacol

Olefin cross metathesis based de novo synthesis of a partially protected L-amicetose and a fully protected L-cinerulose derivative

• Bernd Schmidt and
• Sylvia Hauke

Beilstein J. Org. Chem. 2014, 10, 1023–1031, doi:10.3762/bjoc.10.102

• conditions a chemoselective acetalization of the aldehyde, leading to 23 which was isolated in 52% yield. A similar result was obtained with Pd(OH)2/C (Table 4, entry 2). In situ formed Pd on charcoal [67], prepared from 0.5 mol % of Pd(OAc)2 as a precursor, gave an inseparable mixture of starting material

• . Chemoselective acetalization of oxidation product 21. Hydrogenation of acetal 23. Supporting Information Supporting Information File 61: Experimental procedures and analytical data. Supporting Information File 62: Copies of 1H and 13C NMR spectra. Acknowledgements Generous financial support by the Deutsche

Synthesis of complex intermediates for the study of a dehydratase from borrelidin biosynthesis

• Frank Hahn,
• Nadine Kandziora,
• Steffen Friedrich and
• Peter F. Leadlay

Beilstein J. Org. Chem. 2014, 10, 634–640, doi:10.3762/bjoc.10.55

• TBS ethers and methyl esters was performed under mildly acidic conditions followed by pig liver esterase-mediated chemoselective hydrolysis. These conditions are compatible with the presence of a coenzyme A or a SNAc thioester, suggesting that they are generally applicable to the synthesis of complex

• carboxylate, which necessitates differentiation of the carboxyl groups at the termini to permit regioselective thioester formation. We decided to avoid late redox transformations. Instead, we achieved differentiation by choice of a chemoselective protection group strategy with removal conditions that are

• set up the three stereogenic centres. The construction of the backbone was accomplished by anti-selective aldol reaction or olefination by using the respective phosphonates or phosphoranes. A notable achievement was the development of a chemoselective, mild protection strategy, which is based on an

Direct and indirect single electron transfer (SET)-photochemical approaches for the preparation of novel phthalimide and naphthalimide-based lariat-type crown ethers

• Dae Won Cho,
• Patrick S. Mariano and
• Ung Chan Yoon

Beilstein J. Org. Chem. 2014, 10, 514–527, doi:10.3762/bjoc.10.47

• demonstrate that the zwitterionic biradical intermediates generated in these reactions by photoinduced intramolecular SET undergo highly chemoselective SET-desilylation reactions. As such, this type of reactivity profile can be incorporated into the synthesis for the preparation of a wide variety of azacrown

• ethers that possess different types of polyheteroatom containing side chains. Another observation that is related to the synthetic utility of SET-promoted photocyclization reactions driven by chemoselective desilylation of intermediate zwitterionic radicals comes from photochemical investigations of α

Silver and gold-catalyzed multicomponent reactions

• Giorgio Abbiati and
• Elisabetta Rossi

Beilstein J. Org. Chem. 2014, 10, 481–513, doi:10.3762/bjoc.10.46

Concise, stereodivergent and highly stereoselective synthesis of cis- and trans-2-substituted 3-hydroxypiperidines – development of a phosphite-driven cyclodehydration

• Peter H. Huy,
• Julia C. Westphal and
• Ari M. P. Koskinen

Beilstein J. Org. Chem. 2014, 10, 369–383, doi:10.3762/bjoc.10.35

• . However, Pd/C freshly prepared from Pd(OAc)2 and activated charcoal according to Felpin [77] delivered consistent results (reaction time < 3 h). Although the Cbz-cleavage beside a benzyl moiety in alcohols as solvent is known (for selected examples of the chemoselective Cbz-cleavage of Bn, Cbz-protected

Advancements in the mechanistic understanding of the copper-catalyzed azide–alkyne cycloaddition

• Regina Berg and
• Bernd F. Straub

Beilstein J. Org. Chem. 2013, 9, 2715–2750, doi:10.3762/bjoc.9.308

A protecting group-free synthesis of the Colorado potato beetle pheromone

• Zhongtao Wu,
• Manuel Jäger,
• Jeffrey Buter and
• Adriaan J. Minnaard

Beilstein J. Org. Chem. 2013, 9, 2374–2377, doi:10.3762/bjoc.9.273

• decemlineata, has been developed based on a Sharpless asymmetric epoxidation in combination with a chemoselective alcohol oxidation using catalytic [(neocuproine)PdOAc]2OTf2. Employing this approach, the pheromone was synthesized in 3 steps, 80% yield and 86% ee from geraniol. Keywords: aggregation pheromone

• the secondary alcohol at C-2. The synthesis by Faraldos runs via epoxidation of fluoronerol, subsequent acetylation of the alcohol and solvolysis. In 2010, Waymouth reported the chemoselective, catalytic oxidation of glycerol to dihydroxyacetone (Scheme 1) using catalytic [(neocuproine)PdOAc]2OTf2 (2

• ) in the presence of either benzoquinone or air as the terminal oxidant [12]. More recently, the transformation of unprotected vicinal polyols to α-hydroxy ketones was achieved by regio- and chemoselective oxidation using catalyst 2 [13]. We used this method for the catalytic regioselective oxidation

Towards stereochemical control: A short formal enantioselective total synthesis of pumiliotoxins 251D and 237A

• Jie Zhang,
• Hong-Kui Zhang and
• Pei-Qiang Huang

Beilstein J. Org. Chem. 2013, 9, 2358–2366, doi:10.3762/bjoc.9.271

• steps), from which only the major product 16 was isolated (Scheme 6). For the chemoselective debenzylation, lithium naphthalenide (LN) was used [48]. To our disappointment, attempted cleavage of the benzyl group by LN (THF, −40 °C to rt, 2 h) gave the desired 18 in only 20% yield along with 60% of the

Gold(I)-catalyzed enantioselective cycloaddition reactions

• Fernando López and
• José L. Mascareñas

Beilstein J. Org. Chem. 2013, 9, 2250–2264, doi:10.3762/bjoc.9.264

• carbophilicity, low oxophilicity and high oxidation potential between gold(I) and gold(III) have shown a unique potential to unveil novel types of chemoselective and stereoselective cycloadditions involving alkynes, allenes or alkenes [24][25][26]. A lot of interest has been directed to the development of these

• enantioselectivity. Cycloadditions initiated by activation of allenes Gold(I) catalysts can efficiently activate allenes in a highly chemoselective way, triggering the formation of allenyl cationic species. Different structures have been proposed to represent these gold-activated allene complexes, including η2

A concise enantioselective synthesis of the guaiane sesquiterpene (−)-oxyphyllol

• Martin Zahel and
• Peter Metz

Beilstein J. Org. Chem. 2013, 9, 2028–2032, doi:10.3762/bjoc.9.239

• shown in Scheme 2, we first planned to use the known diol 7, which is available by diastereoselective dihydroxylation of 4 [6]. Since a chemoselective deoxygenation of the secondary alcohol of 7 would give rise to the desired intermediate 3, we investigated a radical defunctionalization strategy [8]. To

A practical synthesis of long-chain iso-fatty acids (iso-C₁₂–C₁₉) and related natural products

• Mark B. Richardson and
• Spencer J. Williams

Beilstein J. Org. Chem. 2013, 9, 1807–1812, doi:10.3762/bjoc.9.210

• -methylpalmitic acid, and 2-oxo-14-methylpentadecane. Keywords: chemoselective reduction; Evans’ auxiliary; Grignard addition; homologation; ionic hydrogenation; Introduction Long-chain iso-fatty acids occur in a broad range of organisms, and are especially abundant in bacteria where, through incorporation into

A Lewis acid-promoted Pinner reaction

• Dominik Pfaff,
• Gregor Nemecek and
• Joachim Podlech

Beilstein J. Org. Chem. 2013, 9, 1572–1577, doi:10.3762/bjoc.9.179

• highly chemoselective; phenols were not acylated by these conditions and were re-isolated with high yields (Table 2, entries 12–14). In this context we tested 4-(2-hydroxyethyl)phenol (53) containing an aliphatic and a phenolic hydroxy function in the reaction with acetonitrile and benzyl cyanide

• . Apparently the double silylation is not possible with electron-deficient substrates. Conclusion The Lewis acid-promoted Pinner reaction is a mild and chemoselective alternative for the synthesis of carboxylic esters starting with alcohols and nitriles. The esterification of primary aliphatic alcohols is

A reductive coupling strategy towards ripostatin A

• Kristin D. Schleicher and
• Timothy F. Jamison

Beilstein J. Org. Chem. 2013, 9, 1533–1550, doi:10.3762/bjoc.9.175

• obtained for either of the individual steps from the methyl series that it replaced. The cleavage of TMSE β-ketoesters with TBAF·3H2O has been described in the literature as a chemoselective method for decarboxylation in the presence of other types of β-ketoesters [64]. Comparable yields for the

Metal-free aerobic oxidations mediated by N-hydroxyphthalimide. A concise review

• Lucio Melone and
• Carlo Punta

Beilstein J. Org. Chem. 2013, 9, 1296–1310, doi:10.3762/bjoc.9.146

• in acetophenone originated from molecular oxygen, by conducting the oxygenation in the presence of 18O2. Finally, Inoue and co-workers reported an efficient C(sp3)–N bond-forming method consisting of the chemoselective conversion of C(sp3)–H bonds in the presence of stoichiometric amounts of dialkyl

Study on the total synthesis of velbanamine: Chemoselective dioxygenation of alkenes with PIFA via a stop-and-flow strategy

• Huili Liu,
• Kuan Zheng,
• Xiang Lu,
• Xiaoxia Wang and
• Ran Hong

Beilstein J. Org. Chem. 2013, 9, 983–990, doi:10.3762/bjoc.9.113

• 321004, China 10.3762/bjoc.9.113 Abstract A “stop-and-flow” strategy was developed for the chemoselective dioxygenation of alkenes with a PIFA-initiated cyclization. This method is conceived for the desymmetrization of seco-diene, and a series of substituted 5-hydroxymethyl-γ-lactones were constructed

• ) [25]. The terminal alkene 6 can be disconnected to give amide 7, which may be derived from 2-bromotryptamine 9 and seco-diene 10. Clearly, the chemoselective dioxygenation of 10 is the main theme in our synthetic endeavor. From here, we expect that current synthetic methods may provide a general basis

• halogen lactonization, as an emerging area, also attracted a lot of attention in recent years [42][43][44]. The two terminal alkenes in compound 10 pose a challenge for chemoselective dioxygenation or iodolactonization. To address this problem, we turn our attention to differentiating the two types of

Reductions of aldehydes and ketones with a readily available N-heterocyclic carbene borane and acetic acid

• Vladimir Lamm,
• Xiangcheng Pan,
• Tsuyoshi Taniguchi and
• Dennis P. Curran

Beilstein J. Org. Chem. 2013, 9, 675–680, doi:10.3762/bjoc.9.76

• procedure. Chemoselective reductions were also readily achieved under the present reaction conditions (Scheme 3). Treatment of a mixture of aldehyde 6 (0.5 mmol) and ketone 19 (0.5 mmol) with 1 (0.25 mmol) and acetic acid (1 equiv) in EtOAc exclusively provided the primary alcohol 13 in 95% yield, while the

• ketone 19 was intact (<5% conversion to 26). The reduction of 4-acetylbenzaldehyde (34) was also chemoselective and afforded only 4-acetylbenzyl alcohol (35) in 79% yield. Conclusion In summary, we have shown that acetic acid is a good activator for the reductions of aldehydes and ketones by stable NHC

• , 94.2 mg, 93%) as a colorless oil. 11B NMR studies of boron products from 1 and acetic acid with and without aldehyde 2. aIn C6D6; bunreacted aldehyde remained. Aldehydes and ketones are reduced by 1 when silica gel is added. Pilot reduction of aldehyde 2 with 1 and acetic acid. Chemoselective

Asymmetric synthesis of a highly functionalized bicyclo[3.2.2]nonene derivative

• Toshiki Tabuchi,
• Daisuke Urabe and
• Masayuki Inoue

Beilstein J. Org. Chem. 2013, 9, 655–663, doi:10.3762/bjoc.9.74

• selective activation of acrolein in the presence of the Lewis-basic allylic oxygen was a prerequisite to the successful formation of 8. We anticipated that bulky trialkylsilyl triflates would function as such chemoselective Lewis acids, because the activation of the TBS-connected oxygen of 7 by the silyl

NHC-catalysed highly selective aerobic oxidation of nonactivated aldehydes

• Lennart Möhlmann,
• Stefan Ludwig and
• Siegfried Blechert

Beilstein J. Org. Chem. 2013, 9, 602–607, doi:10.3762/bjoc.9.65

• of aldehydes to the corresponding acids or esters. The reaction proceeds under metal-free conditions by using N-heterocyclic carbenes as organocatalysts in combination with environmentally friendly oxygen as the terminal oxidation agent. Keywords: aerobic oxidation; chemoselective oxidation; metal

• mild method for more interesting chemoselective transformations. Therefore, several substrates were oxidised under our conditions bearing either a second alcohol or aldehyde functionality. Desymmetrization of dialdehydes by selective oxidation is an important challenge, since symmetric dialdehydes are

Efficient Cu-catalyzed base-free C–S coupling under conventional and microwave heating. A simple access to S-heterocycles and sulfides

• Silvia M. Soria-Castro and
• Alicia B. Peñéñory

Beilstein J. Org. Chem. 2013, 9, 467–475, doi:10.3762/bjoc.9.50

• ), this Cu-catalyzed C–S coupling reaction being highly chemoselective for aryl iodides. In comparison with the already reported procedure for the preparation of S-aryl thioacetates by Pd catalysis [51][56], the methodology herein described has the advantages of using a lower-cost copper salt and a stable

Asymmetric desymmetrization of meso-diols by C₂-symmetric chiral 4-pyrrolidinopyridines

• Hartmut Schedel,
• Keizo Kan,
• Yoshihiro Ueda,
• Kenji Mishiro,
• Keisuke Yoshida,
• Takumi Furuta and
• Takeo Kawabata

Beilstein J. Org. Chem. 2012, 8, 1778–1787, doi:10.3762/bjoc.8.203

• ] and the chemoselective monoacylation of linear diols [17]. Here, we report the asymmetric desymmtrization of meso-diols by C2-symmetric PPY catalysts [20]. The effects of the functional side chains at C(2) and C(5) on the efficiency of the asymmetric desymmetrization are discussed. Some of the results

Copper-catalyzed CuAAC/intramolecular C–H arylation sequence: Synthesis of annulated 1,2,3-triazoles

• Rajkumar Jeyachandran,
• Harish Kumar Potukuchi and
• Lutz Ackermann

Beilstein J. Org. Chem. 2012, 8, 1771–1777, doi:10.3762/bjoc.8.202

• catalyst for two mechanistically distinct transformations for the synthesis of fully substituted annulated 1,2,3-triazoles as well as for twofold N–H/C–H bond arylations. Notable features of our strategy include (i) the development of a chemoselective C–H arylation-based three-component reaction, as well

• catalytic efficacy. Subsequently, we explored the extension of this approach to the development of a chemoselective three-component one-pot reaction. Thus, we found that alkyl bromides 2 could be directly employed as user-friendly substrates for the in situ formation of the corresponding organic azides

• , a variety of annulated 1,2,3-triazoles 4 were obtained, featuring six- or seven-membered rings as key structural motifs. It is particularly noteworthy that the copper-catalyzed transformation enabled the formation of one C–C and three C–N bonds in a chemoselective manner, and thereby provided atom

Palladium-catalyzed dual C–H or N–H functionalization of unfunctionalized indole derivatives with alkenes and arenes

• Gianluigi Broggini,
• Egle M. Beccalli,
• Andrea Fasana and
• Silvia Gazzola

Beilstein J. Org. Chem. 2012, 8, 1730–1746, doi:10.3762/bjoc.8.198

• -methyl-2-butene. Proposed mechanism of the N-indolyl prenylation. Regioselective arylation of indoles by dual C–H functionalization. Plausible mechanism of the selective indole arylation. Chemoselective cyclization of N-allyl-1H-indole-2-carboxamide derivatives. Intramolecular annulations of

Organocatalytic tandem Michael addition reactions: A powerful access to the enantioselective synthesis of functionalized chromenes, thiochromenes and 1,2-dihydroquinolines

• Chittaranjan Bhanja,
• Satyaban Jena,
• Sabita Nayak and
• Seetaram Mohapatra

Beilstein J. Org. Chem. 2012, 8, 1668–1694, doi:10.3762/bjoc.8.191

• -mercaptobenzaldehydes 36 and α,β-unsaturated cyclic ketones 38 proceeded in a highly chemoselective fashion, furnishing the corresponding products 39 in high yield and with moderate to good ee. The mechanism proposed involves the same iminium activation (Scheme 18) of the α,β-unsaturated cyclic ketones by the chiral

Regioselective synthesis of 7,8-dihydroimidazo[5,1-c][1,2,4]triazine-3,6(2H,4H)-dione derivatives: A new drug-like heterocyclic scaffold

• Nikolay T. Tzvetkov,
• Harald Euler and
• Christa E. Müller

Beilstein J. Org. Chem. 2012, 8, 1584–1593, doi:10.3762/bjoc.8.181

• - and chemoselective reaction; thionation; X-ray structure; Introduction Imidazotriazines represent an important class of condensed heterobicycles that display a variety of significant biological activities, including anticancer [1], antimicrobial [2], anti-inflammatory [3] and neuroprotective [4