Kinetics and mechanism of vanadium catalysed asymmetric cyanohydrin synthesis in propylene carbonate

• Michael North and
• Marta Omedes-Pujol

Beilstein J. Org. Chem. 2010, 6, 1043–1055, doi:10.3762/bjoc.6.119

• gives unprotected cyanohydrins which are prone to racemization. Pre-eminent amongst the synthetic catalysts are metal(salen) complexes, especially those based on titanium (1) and vanadium (2) [1] (Figure 1). Titanium complex 1 will catalyse the asymmetric addition of TMSCN to aromatic aldehydes with 80

• asymmetric addition of TMSCN [26][27][28] and KCN [13] to aldehydes and are more enantioselective, but less reactive than the titanium based catalyst 1. Complexes 1 and 2 have been commercialized [10][29][30], immobilized to facilitate their recycling [31][32][33][34][35][36][37][38][39][40][41][42][43] and

• used by other groups as part of synthetic studies [44][45][46]. Mechanistically, the mode of action of catalyst 1 is well understood [15][20][47][48][49], involving a bimetallic transition state in which one titanium atom acts as a Lewis acid, coordinating to the aldehyde, and the other forms a

Solvent-free and time-efficient Suzuki–Miyaura reaction in a ball mill: the solid reagent system KF–Al₂O₃ under inspection

• Franziska Bernhardt,
• Ronald Trotzki,
• Tony Szuppa,
• Achim Stolle and
• Bernd Ondruschka

Beilstein J. Org. Chem. 2010, 6, No. 7, doi:10.3762/bjoc.6.7

• titanium silicalite, TiSiO4, showed moderate conversions in the range of basic γ-Al2O3 SRS3. Contrary to microwave-assisted reactions, MgO showed only little conversion when used as a base under ball milling conditions [34], whereas neutral oxides SiO2 and CeO2 did not show any conversion. Since the

Three step synthesis of single diastereoisomers of the vicinal trifluoro motif

• Vincent A. Brunet,
• Alexandra M. Z. Slawin and
• David O'Hagan

Beilstein J. Org. Chem. 2009, 5, No. 61, doi:10.3762/bjoc.5.61

• reactions following Sharpless’ methodology [16]. The anti-epoxy alcohols were easily generated, however it proved more difficult to prepare the syn-epoxides cleanly. Treatment with titanium isopropoxide (Ti(OiPr)4) and D-diisopropyl tartrate (D-DIPT) favoured formation of the anti-α,β-epoxy alcohols. In the

The efficient synthesis of dibenzo[d,d′]benzo[1,2-b:4,3-b′]dithiophene and cyclopenta[1,2-b:4,3-b′]bis(benzo[d]thiophen)-6-one

• Zhihua Wang,
• Sheng Zhu,
• Jianwu Shi and
• Hua Wang

Beilstein J. Org. Chem. 2009, 5, No. 55, doi:10.3762/bjoc.5.55

• intramolecular McMurry reaction of 4. We found that the reactivity of elemental titanium is crucial in this step and that the Ti(0) must be freshly prepared from zinc dust, pyridine and TiCl4 in THF. By following standard procedures [19][20][21], the title compound 1 was obtained in 66% yield. The overall yield

Green oxidations: Titanium dioxide induced tandem oxidation coupling reactions

• Vineet Jeena and
• Ross S. Robinson

Beilstein J. Org. Chem. 2009, 5, No. 24, doi:10.3762/bjoc.5.24

• Vineet Jeena Ross S. Robinson Department of Chemistry, University of KwaZulu-Natal, Scottsville, Pietermaritzburg, 3209, South Africa 10.3762/bjoc.5.24 Abstract The application of titanium dioxide as an oxidant in tandem oxidation type processes is described. Under microwave irradiation

• , quinoxalines have been synthesized in good yields from the corresponding α-hydroxyketones. Keywords: quinoxalines; tandem oxidation process; titanium dioxide; Introduction Titanium dioxide has found widespread industrial application ranging from whiteners in paint [1], and additives in food [2], to UV

• chemistry point of view, titanium dioxide’s main use has been to oxidize alcohols to its corresponding carbonyl derivatives which has been reported many times [8][9][10]. Titanium dioxide has also been used to synthesize dihydropyrazines [11], piperazines [12], and quinoxalines [13] although in low yields

Zeolite catalyzed solvent- free one-pot synthesis of dihydropyrimidin- 2(1H)-ones – A practical synthesis of monastrol

• Mukund G. Kulkarni,
• Sanjay W. Chavhan,
• Mahadev P. Shinde,
• Dnyaneshwar D. Gaikwad,
• Ajit S. Borhade,
• Attrimuni P. Dhondge,
• Yunnus B. Shaikh,
• Vijay B. Ningdale,
• Mayur P. Desai and
• Deekshaputra R. Birhade

Beilstein J. Org. Chem. 2009, 5, No. 4, doi:10.3762/bjoc.5.4

• under solvent-free conditions. The well-known titanium silicate TS-1 (also known as titanium silicalite) [42] is a widely used heterogeneous catalyst. Therefore we decided to explore its suitability in the Biginelli reaction. For this purpose, a mixture of an aldehyde 1 (1 mmol), ethyl acetoacetate (2

• , 182, 265. Monastrol (4n). General procedure for the synthesis of DHPMs. Titanium silicate (TS-1) catalyzed synthesis of DHPMs. Supporting Information Supporting Information File 3: 13C NMR spectra of compounds 4a–4p Supporting Information File 4: Experimental procedures for compounds 4a–4p

Recent progress on the total synthesis of acetogenins from Annonaceae

• Nianguang Li,
• Zhihao Shi,
• Yuping Tang,
• Jianwei Chen and
• Xiang Li

Beilstein J. Org. Chem. 2008, 4, No. 48, doi:10.3762/bjoc.4.48

• , Pagenkopf’s group reported the total synthesis of bullatacin (311) in an efficient route from commercial starting materials (Scheme 44) [105]. The bis(THF) core 319 was constructed from bis-epoxide 318 through double allylation and oxidative cyclization. Then titanium acetylide 320 was reacted with bis(THF

Synthesis of imidazol- 1-yl-acetic acid hydrochloride: A key intermediate for zoledronic acid

• Santosh Kumar Singh,
• Narendra Manne,
• Purna Chandra Ray and
• Manojit Pal

Beilstein J. Org. Chem. 2008, 4, No. 42, doi:10.3762/bjoc.4.42

• -acetic acid hydrochloride was achieved via N-alkylation of imidazole using tert-butyl chloroacetate followed by a non-aqueous ester cleavage of the resulting imidazol-1-yl-acetic acid tert-butyl ester in the presence of titanium tetrachloride. The synthesized imidazol-1-yl-acetic acid hydrochloride was

• NMR (75 MHz, CDCl3) δ 27.7, 48.6, 82.9, 119.8, 129.2, 137.7, 166.3; MS (m/z) 183.0 [M+1, 100%], 127.0. Preparation of imidazol-1-yl-acetic acid hydrochloride (6) To a solution of imidazol-1-yl-acetic acid tert-butyl ester (2) (10.0 g, 0.05 mol) in dichloromethane (100 mL) was added titanium

Stereoselective synthesis of (2S,3S,4Z)-4-fluoro- 1,3-dihydroxy- 2-(octadecanoylamino)octadec- 4-ene, [(Z)-4-fluoroceramide], and its phase behavior at the air/water interface

• Gergana S. Nikolova and
• Günter Haufe

Beilstein J. Org. Chem. 2008, 4, No. 12, doi:10.3762/bjoc.4.12

• provided the desired tert-butyl imino acid ester 5 as a mixture with the ethyl imino acid ester 6 (formed due to a partial transesterification of 4 with the titanium reagent) and four non-identified compounds (among them most likely diastereomers of the title compounds) in a ratio of 57:28:7:1:2:5

• -fluoroceramide (2b) at the air/water interface a >99% pure compound was used. The diastereoselectivity of the aldol reaction, described above, is controlled by the formation of a titanium enolate, which may follow the mechanism we propose in Scheme 2. The iminoglycinate 4 is deprotonated with Et3N to the

• resonance stabilized anion I. ClTi(OEt)3 coordinates the carbonyl oxygens of 4 and 3 in a six membered Zimmermann-Traxler transition state II. The resulting structure of the titanium alcoholate III shows the erythro-configuration of the tert-butyl amino acid ester 7 and its derivatives 8 and 9. The absolute

Total synthesis of the indolizidine alkaloid tashiromine

• Stephen P. Marsden and
• Alison D. McElhinney

Beilstein J. Org. Chem. 2008, 4, No. 8, doi:10.1186/1860-5397-4-8

• structure, including radical cyclisations [3]; nucleophilic addition to imines [5][14][15]; electrophilic alkylation of pyrroles [7][13]; alkylation of enamines [6], β-amino esters [8] and pyrrolidinyllithiums [12]; stereoselective reduction of enamines [4][9] and pyridinium salts [11]; and titanium

Facile synthesis of two diastereomeric indolizidines corresponding to the postulated structure of alkaloid 5,9E- 259B from a Bufonid toad (Melanophryniscus)

• Angela Nelson,
• H. Martin Garraffo,
• Thomas F. Spande,
• John W. Daly and
• Paul J. Stevenson

Beilstein J. Org. Chem. 2008, 4, No. 6, doi:10.1186/1860-5397-4-6

• as a single diastereoisomer. It is likely that allylic strain of the lactam carbonyl group leads to the alkyl group preferentially occupying a pseudo-axial position [37][38][39][40]. Reaction of N,O-acetal 2 with trimethylallyl silane and titanium tetrachloride at room temperature for two days gave

Combining two-directional synthesis and tandem reactions, part 11: second generation syntheses of (±)-hippodamine and (±)-epi-hippodamine

• Annabella F. Newton,
• Martin Rejzek,
• Marie-Lyne Alcaraz and
• Robert A. Stockman

Beilstein J. Org. Chem. 2008, 4, No. 4, doi:10.1186/1860-5397-4-4

• entry 6 showed reduction of the ketone to the alcohol (by 1H NMR), and entry 5 using the Hantzsch ester showed no reaction at all. It was found that addition of ammonia in ethanol with titanium ethoxide [15] for 14 hours, followed by addition of sodium borohydride and stirring at room temperature for a

A convenient allylsilane- N-acyliminium route toward indolizidine and quinolizidine alkaloids

• Roland Remuson

Beilstein J. Org. Chem. 2007, 3, No. 32, doi:10.1186/1860-5397-3-32

• allyltrimethylsilane, sec-butyllithium and titanium tetraisopropoxide with aldehydes. The key step of the synthesis is the intermolecular addition of the allylsilyl functional group of alcohol 8 on the acyliminium ion derived from ethoxycarbamate 9. Treatment of a mixture of ethoxycarbamate 9 and hydroxyallylsilane 8

Photosonochemical catalytic ring opening of α-epoxyketones

• Hamid R. Memarian and
• Ali Saffar-Teluri

Beilstein J. Org. Chem. 2007, 3, No. 2, doi:10.1186/1860-5397-3-2

• ] tribenzylamine (TBA) [20] and 1,3-dimethyl-2-phenylbenzimidazoline (DMPBI) [22][23][24] or thermally induced single electron transfer by electron donating compounds such as samarium diiodide, [25] tributyltin hydride [26] and bis(cyclopentadienyl)titanium(III) chloride. [27] Ring opening reactions of epoxides

Synthesis and glycosidase inhibitory activity of new hexa- substituted C8-glycomimetics

• Olivia Andriuzzi,
• Christine Gravier-Pelletier,
• Gildas Bertho,
• Thierry Prangé and
• Yves Le Merrer

Beilstein J. Org. Chem. 2005, 1, No. 12, doi:10.1186/1860-5397-1-12

• commercially available 2,2-dimethyl-1,3-dioxan-5-one in the presence of titanium(IV) tetra-isopropoxide followed by the cyanoborohydride reduction of the imine intermediate gave the expected N-alkylated aminocyclitol 17 (46% overall yield from 11). Then, simultaneous acidic hydrolysis of all protective groups

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

• titanium-based methylenating reagents was successful, allowing access to 1-substituted allenylsilanes. Conclusion Many novel allenylsilanes may be accessed by alkylidenation of substituted silylketenes. Importantly, for the first time, simple methylenation of silylketenes has been achieved using titanium

• report for the first time the methylenation of silylketenes to give 1-substituted allenylsilanes using titanium-based methodology. Results and Discussion Our investigations began with the preparation of substituted silylketenes 1 as substrates for the alkylidenation chemistry. This was carried out under

• problem, it gave us the encouragement to screen other titanium carbenoid-based methylenating reagents. The Petasis reagent (dimethyltitanocene) [31][32] was our next choice, and we were pleased to find that it afforded modest to excellent yields of the allenylsilanes in reaction with most of the ketene