A scalable synthesis of the (S)-4-(tert-butyl)-2-(pyridin-2-yl)-4,5-dihydrooxazole ((S)-t-BuPyOx) ligand

• Hideki Shimizu,
• Jeffrey C. Holder and
• Brian M. Stoltz

Beilstein J. Org. Chem. 2013, 9, 1637–1642, doi:10.3762/bjoc.9.187

• adventitious moisture for more than one week. Furthermore, chloride 11 proved to be a superior cyclization substrate. A series of bases were screened. Organic amine bases (Table 2, entries 4,5) and sodium hydride (Table 2, entry 6) provided inadequate conversion and low yields, whereas hydroxide and alkoxide

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

• titanium-mediated, alkoxide-directed fragment coupling reaction between vinylcylopropanes and vinyldimethylchlorosilane (Scheme 3, reaction 4) in which the stereochemical outcome of the rearrangement is orchestrated by the adjacent alkoxide, which is believed to direct formation of a tricyclic

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

• dithioacetals. Reactions of hemiacetals with nitrogen nucleophiles are unsuccessful. 1,2-Dioxolan-3-ols (peroxyhemiacetals) undergo Re(VII)-promoted etherification but not allylation. Hydroperoxyacetals (1-alkoxyhydroperoxides) undergo selective exchange of the alkoxide group in the presence of either Re2O7 or

• were curious about the interactions of Re(VII) oxides with hydroperoxyacetals (1-alkoxyhydroperoxides), versatile intermediates available from ozonolysis of alkenes in alcoholic solvents [23][24]. As can be seen in Table 8, Re2O7, Me3SiOReO3 and PTSA all catalyze alkoxide metathesis to furnish a

• moderate yield of a new hydroperoxyacetal. The exchange reaction was observed in several solvents (e.g., CH2Cl2, 1,2-dichloroethane) but was most efficient in acetonitrile. The alkoxide exchange was accompanied by much slower exchange of the peroxide; for example, prolonged reaction (>24 h) of acetal 26 in

Anionic cascade reactions. One-pot assembly of (Z)-chloro-exo-methylenetetrahydrofurans from β-hydroxyketones

• István E. Markó and
• Florian T. Schevenels

Beilstein J. Org. Chem. 2013, 9, 1319–1325, doi:10.3762/bjoc.9.148

• sole base (Scheme 4). In stark contrast, applying this procedure to the keto-alcohol 14 resulted in a mediocre 13% yield of 6, probably due to a rapid retro-aldol reaction of the derived, rather hindered, potassium alkoxide. Applying the LDA/KOt-Bu protocol improved the yield to 41%. It thus transpires

1-n-Butyl-3-methylimidazolium-2-carboxylate: a versatile precatalyst for the ring-opening polymerization of ε-caprolactone and rac-lactide under solvent-free conditions

• Astrid Hoppe,
• Faten Sadaka,
• Claire-Hélène Brachais,
• Gilles Boni,
• Jean-Pierre Couvercelle and
• Laurent Plasseraud

Beilstein J. Org. Chem. 2013, 9, 647–654, doi:10.3762/bjoc.9.73

•  2). The protonation of the formed zwitterionic acylimidazole intermediate by the alcohol initiator followed by the attack of the thereby obtained alkoxide regenerates the carbene species. The chain propagation is by the attack of the newly formed hydroxy-terminated monomer (I) on another

Some aspects of radical chemistry in the assembly of complex molecular architectures

• Béatrice Quiclet-Sire and
• Samir Z. Zard

Beilstein J. Org. Chem. 2013, 9, 557–576, doi:10.3762/bjoc.9.61

• in the radical sense by converting it into a fluoropyridineoxy derivative by reaction of the alkoxide anion with inexpensive 2,6-difluoropyridine [61][62][63][64][65]. In this manner, any allylic alcohol becomes a potential radical allylating agent. This has proved to be a powerful route to complex

Presence or absence of a novel charge-transfer complex in the base-catalyzed hydrolysis of N-ethylbenzamide or ethyl benzoate

• Shinichi Yamabe,
• Wei Guan and
• Shigeyoshi Sakaki

Beilstein J. Org. Chem. 2013, 9, 185–196, doi:10.3762/bjoc.9.22

• intermediate, Int1(es), is formed. At the intermediate, the alkoxide oxygen O(3) is the most anionic. A proton-attach TS, TS2'(es), was obtained. After TS2'(es), a neutral tetrahedral intermediate Int2'(es), is formed. If this intermediate is very stable, it should be in equilibrium with the reactant-like

Synthesis of conformationally restricted glutamate and glutamine derivatives from carbonylation of orthopalladated phenylglycine derivatives

• Esteban P. Urriolabeitia,
• Eduardo Laga and
• Carlos Cativiela

Beilstein J. Org. Chem. 2012, 8, 1569–1575, doi:10.3762/bjoc.8.179

• drop when 2-propanol (2c) or phenol (2f) are used, and moderate yields are obtained (≈40%), whereas no reaction at all is observed for bulky tertiary alcohols, for example when Me3COH is used. In alkoxycarbonylation reactions the nucleophile finally incorporated into the carbonyl group (an alkoxide

Alkoxide-induced ring opening of bicyclic 2-vinylcyclobutanones: A convenient synthesis of 2-vinyl-substituted 3-cycloalkene-1-carboxylic acid esters

• Xiufang Ji,
• Zhiming Li,
• Quanrui Wang and
• Andreas Goeke

Beilstein J. Org. Chem. 2012, 8, 650–657, doi:10.3762/bjoc.8.72

• cyclobutanones 4 undergo stereoselective ring openings by the action of alkoxide ions (t-BuO− or MeO−) to produce novel vicinally disubstituted cycloalkene derivatives 5 and 6 in moderate to high yields. The ring cleavage usually occurs with complete regioselectivity. The accessibility of γ,δ-unsaturated ester

• or acid derivatives makes this transformation a good supplementary method for the well-established Johnson–Claisen rearrangement. Keywords: alkoxide; cyclobutanones; esters; fused ring systems; ring opening; Introduction A great variety of methods are available for the synthesis of cyclobutane

• the C-3 proton (Figure 1). Taking the high degree of ring strain in substrates 4 into account, an alkoxide-promoted ring opening to vicinally functionalized products 5 or 6 was expected. To validate this proposal, the 7-methyl-7-vinyl substituted bicyclo[3.2.0]heptenone 4a was employed as a model

Directed aromatic functionalization in natural-product synthesis: Fredericamycin A, nothapodytine B, and topopyrones B and D

• Charles Dylan Turner and
• Marco A. Ciufolini

Beilstein J. Org. Chem. 2011, 7, 1475–1485, doi:10.3762/bjoc.7.171

• benzamide 56 with sec-BuLi/TMEDA (1.05 equiv, 3 h, −78 °C) and addition of the resulting organolithium agent to 65 was presumed to form the alkoxide 66. In situ treatment of 66 with t-BuLi induced bromine–lithium exchange and cyclization of organolithium species 67 to a product that was believed to be 68

Directed ortho,ortho'-dimetalation of hydrobenzoin: Rapid access to hydrobenzoin derivatives useful for asymmetric synthesis

• Inhee Cho,
• Labros Meimetis,
• Lee Belding,
• Michael J. Katz,
• Travis Dudding and
• Robert Britton

Beilstein J. Org. Chem. 2011, 7, 1315–1322, doi:10.3762/bjoc.7.154

• was not observed for reactions with other electrophiles (see below). In addition, the products from deuterium quenching studies were often accompanied by the formation of varying amounts of the deoxybenzoin 10, which presumably derives from reaction of an alkoxide function in 8 with D2O, followed by

• intermediate aryl lithium 17 (presumably in an aggregated form) may adopt a conformation in which the lithium alkoxide (DMG) and consequently the base (i.e., n-BuLi or its aggregates) are positioned in close proximity to the ortho proton that is to be removed. Alternatively, the intermediate aryl lithium 17

• may undergo rearrangement to the six-membered heterocycle 18, in which the cis-relationship between the distal lithium alkoxide and the unlithiated phenyl ring facilitates the second deprotonation. While the latter proposal is less likely, based on Seebach’s observation that 2-phenylethanol does not

Scaling up of continuous-flow, microwave-assisted, organic reactions by varying the size of Pd-functionalized catalytic monoliths

• Ping He,
• Stephen J. Haswell,
• Paul D. I. Fletcher,
• Stephen M. Kelly and
• Andrew Mansfield

Beilstein J. Org. Chem. 2011, 7, 1150–1157, doi:10.3762/bjoc.7.133

• any observable change in the reaction conversion. Results and Discussion Synthesis of silica monolith and Pd-supported silica monolith catalyst The reaction parameters, such as polymer concentration, acid strength, water content, amount of silicon alkoxide, reaction temperature and reaction time, all

Toward an integrated route to the vernonia allenes and related sesquiterpenoids

• Da Xu,
• Michael A. Drahl and
• Lawrence J. Williams

Beilstein J. Org. Chem. 2011, 7, 937–943, doi:10.3762/bjoc.7.104

• -decalin system. Low energy conformers were identified for these species [59]. The lowest energy conformer gave the greatest torsion angles (~175°) for both the alcohol V and the alkoxide VI, and these approach 180°. For comparison purposes, the cis-hydrindane derivative in entry 3 was also studied [38

• ]. Analogous to entry 2, this system contains an unsaturated site adjacent to the hydroxy/alkoxide. The torsion angles of the scissile bonds for this entry are approximately 163°. Importantly, this compound is known to undergo base-induced fragmentation to give the (E)-alkene in excellent yield [61]. Among the

• angles (~175°), there appears to be a significant difference between the orientation of the ester relative to the adjacent C–C double bond. For the neutral (R = OH) compound, the ester is coplanar with the double bond, whereas the ester is twisted out of planarity for the alkoxide (R = O−). This appears

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

Recent advances in the development of alkyne metathesis catalysts

• Xian Wu and
• Matthias Tamm

Beilstein J. Org. Chem. 2011, 7, 82–93, doi:10.3762/bjoc.7.12

• established a different design strategy for the development of novel alkyne metathesis catalysts. Inspired both by a report of Johnson and co-workers, who found that molybdenum and tungsten nitride complexes 24 with fluorinated alkoxide ligands react with alkynes to generate the corresponding metal

A novel and efficient method to prepare 2-aryltetrahydrofuran-2-ylphosphonic acids

• Vsevolod V. Komissarov,
• Anatoly M. Kritzyn and
• Jouko J. Vepsäläinen

Beilstein J. Org. Chem. 2010, 6, No. 63, doi:10.3762/bjoc.6.63

• conditions [16] or at elevated temperatures [17]. A plausible explanation for the cyclization occurring at room temperature without an alkoxide intermediate would be to invoke anchimeric assistance of the P=O group, which could serve as a general base to facilitate cyclization leading to the formation of 7

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

Solvent- controlled regioselective protection of allyl- 4,6-benzylidene glucopyranosides

• Kerry Ann Ness and
• Marie E. Migaud

Beilstein J. Org. Chem. 2007, 3, No. 26, doi:10.1186/1860-5397-3-26

• allyl ether at the C1 position of the glucoside. It can be postulated that in THF, regioselectivity depends on the relative acidity of the secondary hydroxyl groups and the nucleophilicity of the resulting alkoxide. The acidity is modulated by intramolecular H-bonds while steric effects control the

Conformational rigidity of silicon- stereogenic silanes in asymmetric catalysis: A comparative study

• Sebastian Rendler and
• Martin Oestreich

Beilstein J. Org. Chem. 2007, 3, No. 9, doi:10.1186/1860-5397-3-9

• kinetic resolution of alcohols (Scheme 4). The phosphine-stabilized copper hydride 12 [17] is likely to be the catalytically active species, which is generated by alkoxide exchange (9 → 10) followed by a single catalytic turnover. The actual catalytic cycle then proceeds in a four-step propagation: (i

• metathesis [19] establishing the silicon-oxygen linkage in 5 and regenerating copper hydride 12 after coordination of another phosphine ligand (11 → 12). With steps (ii) and (iii) being reversible and chelate 10 being capable of alkoxide exchange, that is exchange of the optical antipodes of 4, one

Pd-catalysed [3 + 3] annelations in the stereoselective synthesis of indolizidines

• Olivier Y. Provoost,
• Andrew J. Hazelwood and
• Joseph P. A. Harrity

Beilstein J. Org. Chem. 2007, 3, No. 8, doi:10.1186/1860-5397-3-8

• reasons for this difference in catalyst activity are unclear at present, we speculate that n-BuLi may be responsible for the formation of hitherto uncharacterised phosphine ligands BunP(OiPr)3-n that promote the annelation over simple P(OiPr)3. Indeed, analogous alkoxide substitution reactions of

Investigation of acetyl migrations in furanosides

• O. P. Chevallier and
• M. E. Migaud

Beilstein J. Org. Chem. 2006, 2, No. 14, doi:10.1186/1860-5397-2-14

• acetyl moieties. Such direct transesterification is intermolecular and while it has been observed in nucleoside-phosphoramidite and glycoside chemistry,[20][21][22][23] this alkoxide-promoted intermolecular acetyl migration process has been overlooked in furanosides. The isolated quantities of 1c and 1d

• , pyridine, DMAP (98%). Synthesis of riboside 5. a) BnBr, NaH, THF (82%); b) TBAF, THF (84%); c) PivCl, pyridine/DCM, DMAP (95%); d) TFA/H2O (8/2) (78%); e) MeOH, H2SO4 (73%); f) MeONa/MeOH (85%); g) TBDMSCl, pyridine/DCM, DMAP (78%); h) Ac2O, pyridine, DMAP(98%). Alkoxide promoted transesterification. 1H

Reagent controlled addition of chiral sulfur ylides to chiral aldehydes

• Varinder K. Aggarwal and
• Jie Bi

Beilstein J. Org. Chem. 2005, 1, No. 4, doi:10.1186/1860-5397-1-4

• earlier studies we had established that the degree of reversibility in betaine formation could be influenced by the degree of solvation of the intermediate alkoxide. The initially formed betaine 9 with charges gauche to each other can either undergo bond rotation to betaine 10 followed by ring closure to

• give the epoxide 7a or reversion to the ylide and the aldehyde. Solvation of the alkoxide 9 reduces the barrier to bond rotation rendering reactions less reversible. We therefore examined the same reactions in the presence of LiCl (Table 1, entries 4, 6). Now increased C1 selectivity (C1(R):C1(S), 96:4

• that influenced reversibility in betaine formation included ylide stability, solvation of the metal alkoxide and steric hindrance around the aldehyde and ylide.[2] We now add another factor to this growing list: stereochemistry of the aldehyde. Evidently, in one isomer, the groups between the aldehyde