Synthesis of 2a,8b-Dihydrocyclobuta[a]naphthalene-3,4-diones

• Kerstin Schmidt and
• Paul Margaretha

Beilstein J. Org. Chem. 2010, 6, No. 76, doi:10.3762/bjoc.6.76

• . In the same experiment with 1c, the MeO-group apparently tends to increase the efficiency in photodimerization vs mixed photocycloaddition, otherwise there is no obvious explanation for this result. Experimental 1. General. Acetals 1 were synthesized according to [8]. Both 1b, m.p. 60–62 °C, and 1c

Acid catalyzed cyclodimerization of 2,2-bis(trifluoromethyl)-4-alkoxy-oxetanes and -thietanes. Synthesis of 2,2,6,6-tetrakis(trifluoromethyl)-4,8-dialkoxy-1,5-dioxocanes and 3,3,7,7-tetrakis(trifluoromethyl)-9-oxa-2,6-dithia-bicyclo[3.3.1]nonane

• Viacheslav A. Petrov and
• Will Marshall

Beilstein J. Org. Chem. 2010, 6, No. 46, doi:10.3762/bjoc.6.46

• products. Clean and spontaneous reaction with alcohols is another interesting transformation of oxetanes described in this paper. The reaction leads to high yield formation of the corresponding acetals (CF3)2C(OH)CH2CH(OR)OR′. Structurally related 2,2-bis(trifluoromethyl)-4-R-thietanes (R = i-C3H7O, t

• alcohols in the absence of the catalyst. The reaction leads to a ring opening with the formation of the corresponding acetals of 4,4,4-trifluoro-3-(trifluoromethyl)-3-hydroxybutanal. For example, the addition of 1b or 1c to an excess of methanol results in a fast and mildly exothermic reaction, leading to

• selective formation of acetals 3a or 3b, respectively (Scheme 3). Since the vacuum distillation of 3b lead to decomposition, the isolation of similar products in an analytically pure form was not attempted. However, removal of excess alcohol after the reaction was complete by washing with water afforded

Fused bicyclic piperidines and dihydropyridines by dearomatising cyclisation of the enolates of nicotinyl-substituted esters and ketones

• Heloise Brice,
• Jonathan Clayden and
• Stuart D. Hamilton

Beilstein J. Org. Chem. 2010, 6, No. 22, doi:10.3762/bjoc.6.22

• it into a silyl enol ether 9. Silyl enol ethers and ketene acetals are known to add effectively to pyridinium species in an intermolecular manner [42][43][44][45][46]. Thus 7 was converted to silyl enol ether 9 in excellent yield under standard conditions. A single geometrical isomer was obtained

• chloroformate to activate the pyridine without competing attack by the enolate. Next we extended the reaction to the cyclisation of a δ-nicotinyl butyrate ester 12 encouraged by the observations of Onaka [47], who demonstrated that silyl ketene acetals can be added (in an intermolecular fashion) to electron

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

• arenecarbaldehydes and their corresponding acetals have been used as electrophilic component [7]. While FC alkylations with allyl alcohols and benzyl ethers are likely to have the same carbocationic reaction intermediate, the FC alkylation with arenecarbaldehydes 6 has to be different (Scheme 5). Mechanistic

Synthesis of mesogenic phthalocyanine-C₆₀ donor–acceptor dyads designed for molecular heterojunction photovoltaic devices

• Yves Henri Geerts,
• Olivier Debever,
• Claire Amato and
• Sergey Sergeyev

Beilstein J. Org. Chem. 2009, 5, No. 49, doi:10.3762/bjoc.5.49

• , attempted condensation of 5 and 6a–d gave no desired phthalocyanine derivative. We reasoned that the unprotected OH group in one of the reaction components may affect the condensation, and converted alcohols 6a–d into acetals 9a–d (84–93% yield) by treatment with an excess of methoxyethoxymethyl chloride

2-Phenyl- tetrahydropyrimidine- 4(1H)-ones – cyclic benzaldehyde aminals as precursors for functionalised β²-amino acids

• Markus Nahrwold,
• Arvydas Stončius,
• Anna Penner,
• Beate Neumann,
• Hans-Georg Stammler and
• Norbert Sewald

Beilstein J. Org. Chem. 2009, 5, No. 43, doi:10.3762/bjoc.5.43

• . In the course of this study, an L-asparagine derivative was condensed with benzaldehyde and subsequently converted to orthogonally protected (R)-β2-homoaspartate. Keywords: β2-amino acids; cyclocondensation; diastereoselective alkylation; N,N-acetals; peptidomimetics; ring opening; self-regeneration

• compounds 11b/13. The decisive influence of N-acyl substituents within cyclic five- and six-membered N,N-and N,O-acetals on the stereochemical course of alkylations and ring closure reactions is a long known and frequently observed phenomenon (for an overview, see ref. [50]). The at first sight surprising

• , this novel concept was applied to synthesise orthogonally protected (R)-β2-homoaspartate by means of “self-regeneration of stereogenic centres” (SRS). Asparagine derived benzaldehyde N,N-acetals comparable to 9 have formerly been used as α-alkyl-asparagine precursors [39] and furthermore have been

Acid- mediated reactions under microfluidic conditions: A new strategy for practical synthesis of biofunctional natural products

• Katsunori Tanaka and
• Koichi Fukase

Beilstein J. Org. Chem. 2009, 5, No. 40, doi:10.3762/bjoc.5.40

• important synthetic intermediate for complex N-glycans. Microfluidic reductive opening of sugar 4,6-O-benzylidene acetals The microfluidic conditions can also be applied to an efficient procedure for the reductive opening of 4,6-O-benzylidene acetals [30], a key functional group manipulation toward fragment

• b for our N-glycan synthesis. Reductive opening of sugar 4,6-O-benzylidene acetals by the combination of acid/hydride reagents is one of the most useful transformations in the field of carbohydrate chemistry [49], not only for our current N-glycan case, since the benzyl-protected derivatives at

• either the C4- or C6-hydroxyl can be selectively prepared by the choice of reagent and/or solvent systems [50][51]. The typical procedure of the reductive opening of the acetals involves the very slow addition of the acid to a mixture of the substrate and excess hydride reagent at 0 °C, followed by

Catalytic synthesis of (E)-α,β-unsaturated esters from aldehydes and 1,1-diethoxyethylene

• Rubén Manzano,
• Lidia Ozores,
• Andreas Job,
• Lars Rodefeld and
• Benjamin List

Beilstein J. Org. Chem. 2009, 5, No. 3, doi:10.3762/bjoc.5.3

• treatment with a suitable reagent or catalyst could readily lead to the corresponding unsaturated ester and ethanol or methanol as the only by-product. The use of ketene dialkyl acetals for organic transformations is infrequent [27]. To the best of our knowledge, they have been employed in [2+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

• -opened product 27. Transition states supposed for the regioselective DAR via quinone route. Representative LUMO coeffients of quinones 8 and 12 (a) and their reaction courses with diene 7 (b). Retrosynthesis of kinamycins. Synthesis of quinones 8 and 12 and the acetals 13 and 14. Reagents and conditions

A divergent asymmetric approach to aza-spiropyran derivative and (1S,8aR)-1-hydroxyindolizidine

• Jian-Feng Zheng,
• Wen Chen,
• Su-Yu Huang,
• Jian-Liang Ye and
• Pei-Qiang Huang

Beilstein J. Org. Chem. 2007, 3, No. 41, doi:10.1186/1860-5397-3-41

• to N,O-dibenzyl malimide (4) leads to N,O-acetals 5 in high regioselectivity (Scheme 2), and the subsequent reductive dehydroxylation gives 6 in high trans-diastereoselectivity.[35] On the other hand, treatment of N,O-acteals 5 with an acid furnished enamides E, which can be transformed

• findings are surprising comparing with our recent observations. In our previous investigations, it was observed that the treatment of N,O-acetals 5 with an acid leads to the dehydration products E (Scheme 2), and the two diastereomers of 5 shows different reactivities towards the acid-promoted dehydration

Aroylketene dithioacetal chemistry: facile synthesis of 4-aroyl- 3-methylsulfanyl- 2-tosylpyrroles from aroylketene dithioacetals and TosMIC

• H. Surya Prakash Rao and
• S. Sivakumar

Beilstein J. Org. Chem. 2007, 3, No. 31, doi:10.1186/1860-5397-3-31

• heterocyclic systems, examples of their participation in the cycloaddition reactions are rare. In continuation of our interest on ketene acetals [5][6][7] we considered that 1,3-dipolar cycloaddition of the anion generated from the von Leusen's reagent (p-tolylsulfonyl)methyl isocyanide (TosMIC) 2 to AKDTAs 1

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

• , the acyclic silicon containing chains are simple to synthesise, such as through the formation of either silyl ethers or acetals, may contain a wide range of functionalities and are stable to a range of different reaction conditions and purification techniques. Second, the silicon tethers remain inert

• standard P-K reaction conditions. Analysis of the reaction solution showed that cyclisation had not occurred and the only compound recovered was a quantitative amount of the starting material. ii) Silyl acetal tethers Although silyl ethers have been the predominant ether of choice, silyl acetals have been

• applied as temporary tethers in reactions.[32] Silyl acetals have, for example, been applied to any reactions to which silyl ether have been applied, such as radical, Diels Alder reaction or ring closing metathesis, albeit with varying degrees of success. The advantage of silyl acetals over silyl ethers

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

Methods for the synthesis of polyhydroxylated piperidines by diastereoselective dihydroxylation: Exploitation in the two-directional synthesis of aza-C-linked disaccharide derivatives

• Andrew Kennedy,
• Adam Nelson and
• Alexis Perry

Beilstein J. Org. Chem. 2005, 1, No. 2, doi:10.1186/1860-5397-1-2

• products were converted into the corresponding methyl N,O and O,O acetals 28 and 32. As has previously been observed,[34][35][36][37][38][48][49] the relative configuration of the N,O acetals was completely controlled (2,6cis:2,6trans >95:<5) and that of the O,O acetals was poorly controlled (2,6cis

• .) For the syntheses of the allylated and reduced substrates, the crude products were treated directly with boron trifluoride etherate and either allyltrimethylsilane or triethylsilane. It was possible to switch cleanly to a one-directional synthesis because the N,O acetals were much more susceptible to