Achiral bis-imine in combination with CoCl₂: A remarkable effect on enantioselectivity of lipase-mediated acetylation of racemic secondary alcohol

• K. Arunkumar,
• M. Appi Reddy,
• T. Sravan Kumar,
• B. Vijaya Kumar,
• K. B. Chandrasekhar,
• P. Rajender Kumar and
• Manojit Pal

Beilstein J. Org. Chem. 2010, 6, 1174–1179, doi:10.3762/bjoc.6.134

• were completed within 30 min in most cases. All bis-imines prepared were then screened in combination with CoCl2 for CAL-B mediated acetylation of a racemic secondary alcohol. Thus, 3-(1-hydroxyethyl)phenyl ethyl(methyl)carbamate [(RS)-4], prepared via the reaction of 3-hydroxyacetophenone (6) with N

• . Preparation of racemic 3-(1-hydroxyethyl)phenyl ethyl(methyl)carbamate [(RS)-4] Proposed reaction mechanism of lipase-catalyzed acetylation of racemic alcohol 4. Complete synthesis of rivastigmine. FeCl3-meditated synthesis of bis-imines (3) from (hetero)aryl aldehydes (2). Screening of bis-imines as achiral

Expanding the gelation properties of valine-based 3,5-diaminobenzoate organogelators with N-alkylurea functionalities

• Hak-Fun Chow and
• Chin-Ho Cheng

Beilstein J. Org. Chem. 2010, 6, 1015–1021, doi:10.3762/bjoc.6.114

• esters 2. A mixture of O-succinimidyl carbamate 6 (10.0 mmol) and diisopropylethylamine (1.8 mL, 10.0 mmol) was added to a THF solution (100 mL) of the diamino benzyl ester 4 (2.2 g, 5.0 mmol). The reaction mixture was stirred at 25 °C for 4 h. The insoluble crude solid product was filtered and washed

Insights into the mechanical properties of a silicone oil gel with a ‘latent’ gelator, 1-octadecylamine, and CO₂ as an ‘activator’

• Emiliano Carretti,
• Mathew George and
• Richard G. Weiss

Beilstein J. Org. Chem. 2010, 6, 984–991, doi:10.3762/bjoc.6.111

• mechanical measurements is used to characterize the gel networks and how they respond to temperature and strain. It is shown, for example, that very precise measurements of the gel-to-sol transitions can be obtained from plots of viscosity versus temperature. Keywords: ammonium carbamate; damping factor

• form the gels is simple: bubbling CO2 through a solution of the amine and the liquid for a minute or longer (to ensure complete reaction). The CO2 adds to one amino functionality, forming a carbamate, while a proton of the amine is transferred to a second amine molecule (Scheme 1) [13]. The resultant

• ammonium carbamate from ODA, C18H37NHCO2− +H3NC18H37 (ODA-C), is held together much more strongly, by electrostatic forces, than uncharged latent LMOG molecules. Especially in liquids of low polarity, the electrostatic forces and ion pairing are very strong and they are the basis for the induced self

Synthesis of 6-PEtN-α-D-GalpNAc-(1–>6)-β-D-Galp-(1–>4)-β-D-GlcpNAc-(1–>3)-β-D-Galp-(1–>4)-β-D-Glcp, a Haemophilus influenzae lipopolysacharide structure, and biotin and protein conjugates thereof

• Andreas Sundgren,
• Martina Lahmann and
• Stefan Oscarson

Beilstein J. Org. Chem. 2010, 6, 704–708, doi:10.3762/bjoc.6.80

• was reduced to an amino group, which was protected as a benzyl carbamate (→ 15, 91%). Removal of the TBDMS group with TBAF then gave the tetrasaccharide acceptor 16 (89%). To obtain complete α-selectivity with 2-azido-galactose donors is not trivial. A 4,6-silyl acetal has been suggested as one way to

Recent advances in carbocupration of α-heterosubstituted alkynes

• Ahmad Basheer and
• Ilan Marek

Beilstein J. Org. Chem. 2010, 6, No. 77, doi:10.3762/bjoc.6.77

• the organocopper by the oxygen of the THP completely reversed the regiochemistry of the carbocupration reaction [8]. Ethynyl carbamate is also an oxy-substituted acetylene (and therefore should lead to the branched product). However, the electron-withdrawing group properties of the carbamoyl group

• be very sluggish in carbocupration reactions [1], the carbamate moiety allows reactions with these groups to proceed in good yields. Although much more difficult to prepare, substituted alkynyl derivatives such as propynyl carbamate 12b also reacts easily with organocopper species to afford

• 80/20, Scheme 7). Copper-catalyzed carbomagnesiation could even further increase the efficiency of these reactions. Thus, when ethynyl carbamate 12a was added to a stoichiometric amount of alkylmagnesium halide in Et2O in the presence of 10 mol % CuI, the corresponding (E)-substituted alkene was

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

• many of the signals in the crude 1H NMR spectrum of 14 suggested the existence of either a mixture of diastereoisomers or rotamers caused by restricted rotation of the carbamate group. No dihydropyridine was isolable from this mixture by flash chromatography, probably due to rapid re-aromatisation

• (carbamate C=O), 1677 (ketone C=O); 1H NMR (500 MHz, CDCl3, δH): 7.80 (2H, d, J = 7.5 Hz, Ph-H), 7.41 (1H, t, J = 8.0 Hz, Ph-H), 7.32 (2H, t, J = 8.0 Hz, Ph-H), 6.67 (1H, br, py-H2), 6.54 (1H, br, py-H6), 4.60 (2H, br, py-H5) 3.64 (3H, br, OCH3), 3.33 (2H, m, py-H4 and CH), 2.1–1.3 (6H, br-m, CH2); 13C NMR

• (125 MHz, CDCl3, δC): 202.9 (ketone C=O), 152.2 (carbamate C=O), 137.3, 133.6, 129.1 and 128.8 (aromatic), 123.4 and 123.0 (py-C6), 120.9 and 119.9 (py-C3), 117.1 and 116.8 (py-C2), 108.1 and 107.7 (py-C5), 60.8 (py-C4), 53.8 and 53.7 (OCH3), 38.0 and 37.8 (CH), 32.5 and 32.4 (CH2), 31.7 and 31.6 (CH2

(Pseudo)amide-linked oligosaccharide mimetics: molecular recognition and supramolecular properties

• José L. Jiménez Blanco,
• Fernando Ortega-Caballero,
• Carmen Ortiz Mellet and
• José M. García Fernández

Beilstein J. Org. Chem. 2010, 6, No. 20, doi:10.3762/bjoc.6.20

• , carbamate and thiourea-linked sugars The replacement of amide groups by pseudoamide (NH–C = X)–Y; X, Y = O, N, S) has been widely used in peptide chemistry to induce well-defined secondary structures. In carbohydrate chemistry, the incorporation of pseudoamide-type intersaccharide linkages has an additional

• longer thiourea-linked glycooligomers with linear dendritic and branched architectures, our group has recently reported an efficient synthetic strategy based on the use of AB, AB2 and ABC-type monosaccharide building blocks containing isothiocyanate (A), azido (B) or carbamate groups (C) (Scheme 4) [85

Synthesis of a new class of aminocyclitol analogues with the conduramine D-2 configuration

• Latif Kelebekli,
• Yunus Kara and
• Murat Celik

Beilstein J. Org. Chem. 2010, 6, No. 15, doi:10.3762/bjoc.6.15

• % yield. The introduction of the amino alcohol functionality was achieved by a regio- and stereoselective Pd(0) catalyzed reaction of diol 11 and TsNCO [32]. Thus treatment of the cis-diol 11 in THF with 2 equiv of p-toluenesulfonyl isocyanate gave the corresponding bis-carbamate 12 which was subsequently

• the peroxide bond in 20 with thiourea under very mild conditions gave the cis-diol 21 in 95% yield. Diol 21 in THF was treated with 2 equiv of p-toluenesulfonyl isocyanate to give the intermediate bis-carbamate 22 which was then treated as described above for 12 with the same Pd(0) catalyst to afford

• gel (60 mesh, Merck). Elemental analyses were carried out on a Carlo Erba 1108 model CHNS-O analyzer. The thermal ellipsoid plot of the single crystal X-ray crystallographic structure of 18. 1H NMR NOE spectrum of compound 7. Synthesis of bis-carbamate 12 and oxazolidinone 13. Mechanism of the

Synthetic incorporation of Nile Blue into DNA using 2′-deoxyriboside substitutes: Representative comparison of (R)- and (S)-aminopropanediol as an acyclic linker

• Daniel Lachmann,
• Sina Berndl,
• Otto S. Wolfbeis and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2010, 6, No. 13, doi:10.3762/bjoc.6.13

• evaluate the role of the chirality of the 3-amino-1,2-propanediol linker. Results and Discussion The DNA building block ethynyl (2R)-3-(4,4′-dimethoxytrityl)-2-[(2-cyanoethoxy)(diisopropylamino)phosphinooxy]propylcarbamate (3) contains the propargyl group attached to the glycol part by a carbamate function

• (Scheme 2). In comparison to our earlier synthetic protocols for incorporation of ethidium [29][30], indole [31] and phenothiazine[37] the NH group of the carbamate is less nucleophilic and need not be protected during phosphoramidite synthesis. This facilitates the preparation of DNA building blocks as

Synthesis and binding studies of two new macrocyclic receptors for the stereoselective recognition of dipeptides

• Ana Maria Castilla,
• M. Morgan Conn and
• Pablo Ballester

Beilstein J. Org. Chem. 2010, 6, No. 5, doi:10.3762/bjoc.6.5

• of the C–N single bond in the carbamate protecting groups [37][38]. Upon increasing the temperature of chloroform-d solutions of 1, 2, 15, and 17, the proton signals became sharper and well defined, which is indicative that the chemical exchange due to the conformational equilibria has been

An expedient and new synthesis of pyrrolo[1,2-b]pyridazine derivatives

• Rajeshwar Reddy Sagyam,
• Ravinder Buchikonda,
• Jaya Prakash Pitta,
• Himabindu Vurimidi,
• Pratap Reddy Padi and
• Mahesh Reddy Ghanta

Beilstein J. Org. Chem. 2009, 5, No. 66, doi:10.3762/bjoc.5.66

• -methyl-3-oxo-pentanoic acid phenylamide with tertiary butyl carbazate and subsequent condensation of the resulting carbamate derivative with a chalcone provided a facile new approach to pyrrolo[1,2-b]pyridazine derivatives. Keywords: 1,4-diketone; migration and cyclization; pyrrolo[1,2-b]pyridazine

• ; tertiary butyl carbamate; tertiary butyl carbazate; α,β-unsaturated ketone; Introduction Pyrrolopyridazine derivatives have various biological applications [1][2][3][4][5][6][7][8], and their fluorescent properties have been investigated for potential use in sensors, lasers, and semiconductor devices [9

• [1,2-b]pyridazine-5-carboxylic acid phenylamide 5a. A plausible mechanistic pathway for the formation of compounds 6a–j involves hydrolysis and decarboxylation of carbamate 3, subsequent condensation with chalcone 4a–j to provide alkenyl imine 9, its sequential hydrolysis and decarboxylation, followed

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

• , Universitätsstr. 25, 33615 Bielefeld, Germany 10.3762/bjoc.5.43 Abstract Novel procedures have been developed to condense benzaldehyde effectively with β-amino acid amides to cyclic benzyl aminals. Double carbamate protection of the heterocycle resulted in fully protected chiral β-alanine derivatives. These

• temperature. Despite the success in condensing 3 and benzaldehyde (dimethylacetal), all attempts to condense 3 with closely related acetophenone dimethylketal did not lead to any cyclisation product. To facilitate our selective ring opening concept, the N3-nitrogen of 4 had to be protected as a carbamate

• can be purified by column chromatography, it turned out to be only moderately stable and slowly degraded to Cbz-(R)-β2hAsp(Ot-Bu)-OH, benzaldehyde and tert-butyl carbamate upon prolonged exposure to air moisture. Therefore, unpurified 15 was directly converted to the free amino acid by means of

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

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

• , are derivatives of this first series obtained by elimination of the carbamate at position 10 [25][26]. Mitomycin B, 10, and mitomycin D, 11, possess the opposite absolute configuration of the asymmetric carbon C9. Interestingly, Hornemann proved that this carbon could be easily epimerized to give 9

• synthesis of Vitamin B12 by the groups of Woodward and Eschenmoser [130], this synthesis utilized a powerful methodology developed during this period to make vinylogous amides [131][132]. Pyrrolidinethione 176 was reacted with the dibromoester 177 to give the Z isomer of the vinylogous carbamate 178 (Scheme

• presence of acetic anhydride to give the cis acetamido-acetate 183. The methylene side chain containing the methyl-carbamate was introduced via a Vilsmeier–Haack reaction and the aromatic ring was oxidized with the same method discussed in section 6.2 (vide supra). The synthesis was completed by selective

Synthesis of dihydrophenanthridines by a sequence of Ugi-4CR and palladium- catalyzed intramolecular C-H functionalization

• Florence Bonnaterre,
• Michèle Bois-Choussy and
• Jieping Zhu

Beilstein J. Org. Chem. 2008, 4, No. 10, doi:10.3762/bjoc.4.10

• insensitive to electronic properties of the aromatic ring. Thus, palladium-catalyzed cyclization of 6b, 6c, 6g, 6h, bearing electron-donating or electron-withdrawing groups, afforded the corresponding cyclized products in comparable yields (entries 2, 3, 7, 8). Functional groups such as ester, carbamate

Vinylogous Mukaiyama aldol reactions with 4-oxy-2-trimethylsilyloxypyrroles: relevance to castanospermine synthesis

• Roger Hunter,
• Sophie C. M. Rees-Jones and
• Hong Su

Beilstein J. Org. Chem. 2007, 3, No. 38, doi:10.1186/1860-5397-3-38

• doubt. Attention was then turned to changing the N-protecting group to a carbamate in line with TBSOP 1. The pyrroline precursor 4 (R1 = H, R2 = OMe) was readily prepared via condensation of ethyl E-4-chloro-3-methoxybut-2-enoate with ammonia, and then transformed to carbamates 4c and 4d under the

• raising the energy of the silyloxypyrrole HOMO. However, this still leaves the question of why Casiraghi's TBSOP 1 with an N-carbamate protecting group is so effective compared to our case 5f with the N-benzyl group in which the nitrogen lone pair is more delocalized into the pyrrole ring. Possible

• derivatives using standard conditions ((Boc)2O (4 equiv), THF, DMAP) to give 13 in 90% yield as a crystalline solid. N-Boc lactam 13 was then reduced to lactol 14 with DIBAL-H to afford a mixture of diastereomers in 86% yield, which was reduced with triethylsilane in the presence of BF3·OEt2 to give carbamate

Synthesis of sulfonimidamides from sulfinamides by oxidation with N-chlorosuccinimide

• Olga García Mancheño and
• Carsten Bolm

Beilstein J. Org. Chem. 2007, 3, No. 25, doi:10.1186/1860-5397-3-25

• , the qualitative formation of sulfonimidoyl chloride 2a and its conversion to sulfonimidamide 3a could easily be followed by TLC. Subsequently, the role of the substituent at the sulfinamide nitrogen was examined. The reactivity of N-benzoyl, -benzyl and -tert-butyl carbamate protected sulfinamides 1a

Colchitaxel, a coupled compound made from microtubule inhibitors colchicine and paclitaxel

• Karunananda Bombuwala,
• Thomas Kinstle,
• Vladimir Popik,
• Sonal O. Uppal,
• James B. Olesen,
• Jose Viña and
• Carol A. Heckman

Beilstein J. Org. Chem. 2006, 2, No. 13, doi:10.1186/1860-5397-2-13

• corresponding t-butyl carbamate group [37]. This allowed the acetyl substituent to be removed easily and quantitatively [38]. The amide nitrogen in colchicine (2) was protected with a tert-butoxycarbonyl (t-Boc) group by treatment with an excess of di(tert-butyl)dicarbonate (DCC) in the presence of 4

The oxanorbornene approach to 3-hydroxy, 3,4-dihydroxy and 3,4,5-trihydroxy derivatives of 2-aminocyclohexanecarboxylic acid

• Ishmael B. Masesane,
• Andrei S. Batsanov,
• Judith A. K. Howard,
• Raju Mondal and
• Patrick G. Steel

Beilstein J. Org. Chem. 2006, 2, No. 9, doi:10.1186/1860-5397-2-9

• reduction with Zn/HCl followed by addition of (Boc)2O and a large excess of iPr2NEt. At this stage, confirmation of the correct assignment of the relative stereochemistry for each isomer was realised by an X-ray crystallographic structure determination of the endo carbamate 2b (see Supporting Information

• the literature and our initial experiments followed these precedents. [17][18][19][20] Using carbamate 2b, treatment with LDA or LHMDS appeared, by TLC, to give complete conversion extremely rapidly. However, on workup, considerable amounts of the starting ester were recovered. Similar observations

• values supported by nOe correlations, Figure 1. For example, the amide derivatives of the anti-anti isomer 8 and 9 show distinctive large di-axial couplings for 1-H, 2- H and 3-H. Final confirmation of the stereochemistry was achieved by reduction and deprotection of a single enantiomer of carbamate 4

Total syntheses of oxygenated brazanquinones via regioselective homologous anionic Fries rearrangement of benzylic O-carbamates

• Glaucia Barbosa Candido Alves Slana,
• Mariângela Soares de Azevedo,
• Rosângela Sabattini Capella Lopes,
• Cláudio Cerqueira Lopes and
• Jari Nobrega Cardoso

Beilstein J. Org. Chem. 2006, 2, No. 1, doi:10.1186/1860-5397-2-1

• condensed aromatics. We found this route very attractive and envisaged that by in situ treatment of intermediate 4 with the third equivalent of sec-BuLi, the cyclization to the desired quinone 1a-d would be obtained. One unexpected result was the formation of the phthalide 9 when the dimethoxy carbamate 2d