Dimerization of propargyl and homopropargyl 6-azido- 6-deoxy- glycosides upon 1,3-dipolar cycloaddition

• Nikolas Pietrzik,
• Daniel Schmollinger and
• Thomas Ziegler

Beilstein J. Org. Chem. 2008, 4, No. 30, doi:10.3762/bjoc.4.30

• rings containing two sugar moieties and two 1,2,3-triazole moieties. For instance, such compounds may function as novel ligands for the preparation of metal complexes [24]. Further examples for cyclizations of other azido-alkynyl-glycosides are under investigation. Schematic representation of

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

• silylcuprate with electrophiles ("the silylcuprate strategy") provides new routes for the synthesis of functionalised allylsilanes, which undergo highly stereocontrolled silicon-assisted intramolecular cyclizations leading to three to seven membered ring-formation. Background Organosilicon compounds and in

• to a wide range of functionalised allylsilanes, which are valuable intermediates for carbocyclic annulations. Effectively, the former substrates (containing a nucleophilic allylsilane unit and an electrophilic function) undergo "intramolecular allylsilane terminated" cyclizations when treated with

• reaction between 2 and α,β-unsaturated acid chlorides provides an easy approach to silylated divinyl ketones 9–10 (Scheme 2), which are excellent precursors for silicon-directed Nazarov cyclizations. Acid catalysed electrocyclic closure (TFA, 0–20°C) allows the formation of exocyclic 2-methylenecyclopentan

Do α-acyloxy and α-alkoxycarbonyloxy radicals fragment to form acyl and alkoxycarbonyl radicals?

• Dennis P. Curran and
• Tiffany R. Turner

Beilstein J. Org. Chem. 2006, 2, No. 10, doi:10.1186/1860-5397-2-10

• through mesylates by a standard procedure. Iodides 11a and 11b were stable to heating at 120°C in C6D6 for 24 h, so polar pathways for product formation are not likely in the cyclization experiments described below. The projected mechanism for cyclizations of 11a,b with Bu3SnH in a competition kinetics

• ultimately also result in the formation of 15, but the concentration dependence of this process is not clear since the oxidation step is not fully understood. Based on the mechanism in Figure 4, authentic samples of all products expected from the cyclizations of 11a and 11b were synthesized as shown in

• process begins to break down, so low conversions and yields result. AIBN has been suggested to be an oxidant in related reactions, [9][33] so we conducted a series of individual cyclizations of 11a at 0.01 M with increasing amounts of AIBN. The results of these experiments are summarized in Table 2. If

Efficient synthesis of 5-substituted 2-aryl- 6-cyanoindolizines via nucleophilic substitution reactions

• Eugene V. Babaev,
• Natalya I. Vasilevich and
• Anna S. Ivushkina

Beilstein J. Org. Chem. 2005, 1, No. 9, doi:10.1186/1860-5397-1-9

• open a new way to functionalize the C-5 position (in most cases considered as inactive). The studies of further cyclizations of 5-substituted indolizines involving neighbouring cyano-group and ring position C3 is underway. Note *Characteristics of parent indolizinones 1 a – d were identical to those

Synthesis of 2,6-trans- disubstituted 5,6-dihydropyrans from (Z)-1,5-syn-endiols

• Eric M. Flamme and
• William R. Roush

Beilstein J. Org. Chem. 2005, 1, No. 7, doi:10.1186/1860-5397-1-7

• dihydropyan ent-3. Cyclic ethers of various ring size have been synthesized by the cyclodehydration of diols through the use of oxyphosphonium salts and phosphorane reagents.[18][19][20][21][22][23] We reasoned that because the rate determining step of these cyclizations is believed to be the nucleophilic