Iridium-catalyzed intramolecular [4 + 2] cycloadditions of alkynyl halides

• Andrew Tigchelaar and
• William Tam

Beilstein J. Org. Chem. 2012, 8, 1765–1770, doi:10.3762/bjoc.8.201

• , including homogeneous hydrogenation [1][2], C–H activation [3][4][5], asymmetric ring-opening reactions [6], and a variety of cycloisomerizations [7][8][9][10], and cycloadditions [11][12][13][14][15][16][17][18][19][20]. Traditionally these types of cycloisomerization and cycloaddition reactions are

Synthesis and ring openings of cinnamate-derived N-unfunctionalised aziridines

• Alan Armstrong and
• Alexandra Ferguson

Beilstein J. Org. Chem. 2012, 8, 1747–1752, doi:10.3762/bjoc.8.199

• -diphenylphosphinyl hydroxylamine. The resulting N-unfunctionalised aziridines are shown to be versatile synthetic building blocks that undergo highly selective ring-opening reactions with a wide range of nucleophiles. Keywords: amino acids; aziridination; organocatalysis; ring opening; stereoselectivity

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

• [18][19][20][21][22][23]. Ring-opening reactions of cyclobutanones are expected to be a valuable methodology for vicinal difunctionalization of double bonds. A prerequisite for this reaction to take place is the presence at C-2 of substituents capable of stabilizing the developing vicinal carbanion [6

Molecular rearrangements of superelectrophiles

• Douglas A. Klumpp

Beilstein J. Org. Chem. 2011, 7, 346–363, doi:10.3762/bjoc.7.45

• steps similar to monocationic rearrangements, such as alkyl group shifts, Wagner–Meerwein shifts, hydride shifts, ring opening reactions, and other skeletal rearrangements. This review will describe these types of superelectrophilic reactions. Keywords: dication; rearrangement; superacid

• superelectrophiles are often densely charged species, they are also known for their tendencies to undergo rearrangement and charge migration reactions. These types of conversions will be examined in this review article, including ring opening reactions, carbon–carbon bond shifts, skeletal rearrangements, and charge

• migrations or hydride shifts. Simple Friedel–Crafts type reactions and cyclizations will not be covered. Review Ring opening reactions Several types of superelectrophiles are known to undergo ring opening reactions. The ring opening reaction step can be followed by the reaction with a nucleophile. For

Carbasugar analogues of galactofuranosides: α-O-linked derivatives

• Jens Frigell and
• Ian Cumpstey

Beilstein J. Org. Chem. 2010, 6, 1127–1131, doi:10.3762/bjoc.6.129

• or α-galacto carbapyranose 1,2-epoxides [16]. We considered the reactivity of a diastereomeric epoxide to the α-galacto carbafuranose epoxide 1, i.e., a β-talo epoxide 4, in nucleophilic ring-opening reactions. The same steric and electronic arguments on regioselectivity would predict attack at C1 in

Prins fluorination cyclisations: Preparation of 4-fluoro-pyran and -piperidine heterocycles

• Guillaume G. Launay,
• Alexandra M. Z. Slawin and
• David O'Hagan

Beilstein J. Org. Chem. 2010, 6, No. 41, doi:10.3762/bjoc.6.41

• incorporated into the product generating a C–F bond and a new stereogenic centre. Liberation of fluoride ion from BF3·OEt2 has, for example, been observed in epoxide ring opening reactions [8][9]. This was first recognised in a Prins reaction as an unexpected side reaction by Al-Mutairi et al. [10][11] and was

Iridium-catalyzed asymmetric ring-opening reactions of oxabicyclic alkenes with secondary amine nucleophiles

• Dingqiao Yang,
• Ping Hu,
• Yuhua Long,
• Yujuan Wu,
• Heping Zeng,
• Hui Wang and
• Xiongjun Zuo

Beilstein J. Org. Chem. 2009, 5, No. 53, doi:10.3762/bjoc.5.53

• ring-opening reactions of oxabicyclic alkenes with various aliphatic and aromatic secondary amines are reported for the first time. The reaction gave the corresponding trans-1,2-dihydronaphthalenol derivatives in good yields with moderate enantioselectivities in the presence of 2.5 mol % [Ir(COD)Cl]2

• metal catalysts may be used for asymmetric ring-opening reactions of oxabicyclic alkenes. These include complexes of copper [20][21][22][23][24][25], palladium [14][15][26][27][28][29][30][31], iron [32], and nickel [33][34][35][36]. Recently, we reported for the first time iridium-catalyzed asymmetric

• procedure (I) for the asymmetric ring-opening reactions of oxabenzonorbornadiene 1a with substituted N-alkylaniline: A 5.0 mL round-bottom flask fitted with a reflux condenser was flame-dried under a stream of nitrogen and cooled to room temperature. [Ir(COD)Cl]2 (5.8 mg, 2.5 mol %) and (S)-p-Tol-BINAP

The first preparative solution phase synthesis of melanotan II

• Vladimir V. Ryakhovsky,
• Georgy A. Khachiyan,
• Nina F. Kosovova,
• Elena F. Isamiddinova and
• Andrey S. Ivanov

Beilstein J. Org. Chem. 2008, 4, No. 39, doi:10.3762/bjoc.4.39

• poses a potential problem, due to its susceptibility to base-catalyzed cyclization to aspartimide. Esterification of γ-carboxy group does not fully protect aspartic acid from this unwanted process [25]. Aspartimides are known to readily racemize under basic conditions [26], and undergo ring-opening

• reactions with nucleophiles, leading to formation of a variety of by-products. Thus, attack of nucleophiles yields predominately β-aspartyl peptide derivatives. This deleterious side process usually takes place when the synthesis is based on Fmoc tactics, wherein large excess secondary amines are employed

Desymmetrization of 7-azabicycloalkenes by tandem olefin metathesis for the preparation of natural product scaffolds

• Wolfgang Maison,
• Marina Büchert and
• Nina Deppermann

Beilstein J. Org. Chem. 2007, 3, No. 48, doi:10.1186/1860-5397-3-48

• following two reasons: 1. Azabicycloalkene 7 is easy to synthesize via Diels-Alder reaction.[62] 2. It was assumed to be a good substrate for RORCM because it is strained and has been shown to be susceptible to other desymmetrizing ring opening reactions in the past.[63][64] To generate appropriate

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

• 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