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

• obtained from the "silylcuprate methodology" provides a rapid access to epoxyallylsilanes. Thus, capture of intermediate 2 with enones and later treatment with sulfur ylides afford the epoxyallylsilanes 23–27 (Scheme 5). Despite its synthetic potential, the cyclization of epoxyallylsilanes has not been

• different from that observed for phenyldimethylsilylepoxyallylsilanes of type 23, giving nucleophilic substitution at the most substituted carbon of the epoxide (Scheme 6). [18][19] Three and Four Membered Carbocycles Oxoallylsilanes 4–7, 33 and 34, readily available via silylcuprate addition of 2 to enones

• vinylmagnesium bromide followed by Swern oxidation lead to enones 48. Lewis acid catalysed cyclization of 48 gives methylenecycloheptanones 49 in high yield (Scheme 11). [25] Consequently, oxoallylsilanes 47 can be considered as useful precursors for cycloheptane annulation. Moreover, the presence of an

Multiple hydride reduction pathways in isoflavonoids

• Auli K. Salakka,
• Tuija H. Jokela and
• Kristiina Wähälä

Beilstein J. Org. Chem. 2006, 2, No. 16, doi:10.1186/1860-5397-2-16

• , DIBAH) occurs normally by 1,2-attack, this being a key step in the well known "carbonyl transposition" of 1,3-diketone enol ethers into enones (R3O-CR=CR1-COR2 → R-CO-CR1=CHR2). [11][12][13][14][15] Prior to our work there were no reports on the reduction of isoflavones containing free hydroxy groups

One-pot synthesis of novel 1H-pyrimido[4,5-c][1,2]diazepines and pyrazolo[3,4-d]pyrimidines

• Dipak Prajapati,
• Partha P. Baruah,
• Baikuntha J. Gogoi and
• Jagir S. Sandhu

Beilstein J. Org. Chem. 2006, 2, No. 5, doi:10.1186/1860-5397-2-5

• oxide was reacted with the 1,3-dimethyl-6-hydrazinouracil 1 under the identical condition, we did not observe the formation of pyrimido [4,5-c][1,2]diazepine of the type 3 as we obtained with other enones. Here, we obtained the corresponding pyrimido [4,5-c][1,2]diazepine 4, a tautomeric form of 3 in 90

An exceptional P-H phosphonite: Biphenyl- 2,2'-bisfenchylchlorophosphite and derived ligands (BIFOPs) in enantioselective copper- catalyzed 1,4-additions

• T. Kop-Weiershausen,
• J. Lex,
• J.-M. Neudörfl and
• B. Goldfuss

Beilstein J. Org. Chem. 2005, 1, No. 6, doi:10.1186/1860-5397-1-6

• ][13][14][15][16][17][18] Such asymmetric conjugate additions of diethylzinc to enones are often highly enantioselective, especially with phosphoramidites (amidophosphites) and phosphites. [2][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] These chiral

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

• -carbon partners in [3+2] annulation reactions. Thus, reaction with aldehydes,[7] imines/iminiums,[7][8] enones [9][10][11] and nitrosyl cations [12] leads to dihydrofurans, dihydropyrroles, cyclopentenes and isoxazoles respectively.[13] In most cases the silicon is retained in the final product and can

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

• exploited in the two-directional synthesis of aza-C-linked disaccharide analogues. A two-directional oxidative ring expansion was used to prepare bis-enones such as (2R,6S,2'S)-6-methoxy-2-(6-methoxy-3-oxo-3,6-dihydro-2H-pyran-2-ylmethyl)-1-(toluene-4-sulfonyl)-1,6-dihydro-2H-pyridin-3-one from the

• piperidinyl N,O-acetal should be possible to yield the bis-enones 5. Two-directional diastereoselective reduction (→ 6) and functionalisation would yield the protected aza-C-linked disaccharide analogues 7. Provided that the stereochemical outcome of the reduction and functionalisation steps may be controlled

• . Although it had been possible to isolate trans-30 as a single anomer by careful column chromatography, the bis-enones 26, 28 and 32 were used directly in the reduction step as 66:34 anomeric mixtures. Two-directional Luche[41][42] reduction of the bis-enones 26, 28, trans-30 and 32 was high yielding and