Allylsilanes in the synthesis of three to seven membered rings: the silylcuprate strategy

• Asunción Barbero,
• Francisco J. Pulido and
• M. Carmen Sañudo

Beilstein J. Org. Chem. 2007, 3, No. 16, doi:10.1186/1860-5397-3-16

• -vinylcuprate species toward electrophiles increases their synthetic potential (Scheme 1). [7][8] A large number of electrophiles (alkyl and allyl halides, epoxides, ketones, α,β-unsaturated oxo compounds and acid chlorides, unsaturated nitriles and imines) have been successfully used in this reaction, leading

• the synthesis of spiro[2][5]octanes, an structural moiety of interest in the synthesis of natural products. Alcohols as 40 containing an allylsilane unit, which can be readily obtained by reaction of epoxides with the silylcuprate 2, are excellent synthons for cyclobutane ring-formation. Formation of

• . Intramolecular cyclization of TMS-epoxyallylsilanes. Spiro-cyclopropanation from oxoallylsilanes. Cyclobutane formation from hydroxy-functionalized allysilanes. Cyclobutene formation from vinyltin cuprates and epoxides. Silylcupration of 1,2-propadiene and reaction with α,β-unsaturated nitriles. Cycloheptane

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

• the corresponding γ-lactone. [19] In our recent study, we have used 1-benzyl-2,4,6-triphenylpyridinium tetrafluoroborate (NBTPT) as photocatalyst in a highly diastereoselective ring opening of α-epoxyketones in acetone solution with the formation of 1.3-dioxolanes. [20] Ring opening of epoxides and α

• only in thermal but also in photochemical transformations. Single electron transfer (SET) induced ring opening reactions of epoxides and α-epoxyketones have demonstrated C-C and C-O bond cleavages through photo-induced electron transfer by various electron donors such as triethylamine (TEA), [21

• ] 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

The vicinal difluoro motif: The synthesis and conformation of erythro- and threo- diastereoisomers of 1,2-difluorodiphenylethanes, 2,3-difluorosuccinic acids and their derivatives

• David O'Hagan,
• Henry S. Rzepa,
• Martin Schüler and
• Alexandra M. Z. Slawin

Beilstein J. Org. Chem. 2006, 2, No. 19, doi:10.1186/1860-5397-2-19

• manner, using either cis- or trans- epoxides 3 obtained directly from either the Z- or the E- alkenes. (Scheme 2). Ring opening of the epoxides 3 with HF-amine reagents generate the corresponding threo- and erythro- fluorohydrins 4 in largely a stereoselective manner. The resulting fluorohydrins 4 can

Hydrogenation of aromatic ketones, aldehydes, and epoxides with hydrogen and Pd(0)EnCat™ 30NP

• Steven V. Ley,
• Angus J. P. Stewart-Liddon,
• David Pears,
• Remedios H. Perni and
• Kevin Treacher

Beilstein J. Org. Chem. 2006, 2, No. 15, doi:10.1186/1860-5397-2-15

• well as aromatic epoxides are selectively reduced to the corresponding alcohols under mild conditions using conventional hydrogen in the presence of Pd(0)EnCat™ 30NP catalyst. The reactions were performed at room temperature during 16 hours with high to excellent conversions of the corresponding

• University described the selective reduction of electron deficient and neutral aryl ketones to benzylic alcohols using Pd(0)EnCat™ 30NP as catalyst and a mixture of HCOOH/Et3N as the source of hydrogen [16]. Under these conditions they also achieved the chemoselective hydrogenolysis of aryl epoxides [17

• ]. For these kind of substrates, catalysts based on Ni, Pd, and Pt have been used, and further efforts are directed toward improving the chemoselectivity and regioselectivity of this ring-opening reaction. [18][19] We now demonstrate that aryl aldehydes and ketones as well as aryl epoxides can also

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

• carbamates we then sort to exploit the alkene units to provide a convenient source of poly-hydroxylated cyclohexane β-aminoacids. Consequently, treatment of endo derived hydroxy diene with mCPBA in DCM afforded a separable 9:1 mixture of epoxides 10 and 11 favouring addition syn to the carbamate, Scheme 3

• , palladium mediated reactions of vinyl epoxides are known to proceed with allylic cleavage.[24] Subsequent addition of hydrogen to the intermediate π-allyl palladium complex would provide the desired 4-hydroxy-ACHC derivative. In agreement with this analysis, reaction of the epoxides with hydrogen in the

• afforded the trans β-amino acid derivative 22 as established by NMR experiments. Having prepared the 4,5-cis diol, we turned our attention to the synthesis of the corresponding trans diols. These could be prepared by simple hydrolytic cleavage of epoxides 10–13. In line with this plan, treatment of 12 with

Synthesis of phosphorothioates using thiophosphate salts

• Babak Kaboudin and
• Fatemeh Farjadian

Beilstein J. Org. Chem. 2006, 2, No. 4, doi:10.1186/1860-5397-2-4

• of ammonium acetate/sulfur/acidic alumina under solvent-free conditions using microwave irradiation. [49] This reagent can be used as an efficient reagent for the conversion of epoxides to thiiranes. This ambident nucleophile has two potentially attacking atoms (S or O) and can attack with either of

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

• particular case, due to the hindered conformation of such epoxides as demonstrated by X-ray cristallographic analysis. Conclusion The biological activity of the synthesized glycomimetics has been evaluated towards 24 commercially available glycosidases. The weak observed activities can probably be related to

• epoxidation [35] of the cyclooctenes 1 and 2 (Scheme 2). Thus, treatment of 1 and 2 with meta-chloroperbenzoic acid in the presence of sodium hydrogen carbonate afforded the epoxides 7 and 8 in 91–96% yield. As precedently, because of the C2-axis of symmetry displayed by the L-ido or D-manno-cyclooctenes 1

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

• (dimethylamino)-phosphoranylidene]-phosphoric triamide ethylimine,) [4][5] (sulfur ylide 4) was initially investigated to establish the degree of substrate control. This furnished a mixture of 3 epoxides 7a, 7b, and 7c in a 37:14:49 ratio (Table 1, entry 1). The cis and trans isomers are easily distinguished by

• k9 and k11) was very similar and that the ratio of epoxides obtained was therefore governed by the rates of betaine formation (k1 and k3) which again is determined by the degree of Felkin-Anh/Cornforth control by the substrate (Scheme 5). These experiments showed that in the absence of reagent