Rh-Catalyzed rearrangement of vinylcyclopropane to 1,3-diene units attached to N-heterocycles

• Franca M. Cordero,
• Carolina Vurchio,
• Stefano Cicchi,
• Armin de Meijere and
• Alberto Brandi

Beilstein J. Org. Chem. 2011, 7, 298–303, doi:10.3762/bjoc.7.39

• heating, rearrange [10] to yield a large variety of spirocyclopropanated heterocyclic ketones 4 depending on the nature of the starting nitrone (Scheme 1) [11][12][13][14][15][16][17]. This rather general and convenient access to spirocyclopropane-annelated heterocyclic ketones 4 makes it attractive for

• Discussion The tetrahydropyridones employed in this study were prepared according to published procedures with slight modifications. In particular, oxidation of the tetrahydroquinoline 5 with oxone [38] afforded the nitrone 6 [39][40][41] in 66% yield (Scheme 2, see Supporting Information File 1 for full

• the enantiopure nitrone 10 [42] derived from L-tartaric acid was complete within only 1.5 h at 120–125 °C under microwave (MW) heating and afforded the oxospirocyclopropanes anti-12 and syn-12 in 55% overall yield along with the 1,5-hydrogen shift product 13 (13%) (Scheme 3, see Supporting Information

Addition of lithiated enol ethers to nitrones and subsequent Lewis acid induced cyclizations to enantiopure 3,6-dihydro-2H-pyrans – an approach to carbohydrate mimetics

• Fabian Pfrengle and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2010, 6, No. 75, doi:10.3762/bjoc.6.75

• is in line with the addition of other nucleophiles to nitrone 2a [9][10][11]. The configurations of compounds 4 could be unambiguously assigned by X-ray crystallographic analysis of an aminopyran derivative derived from anti-4b (compound 29, Scheme 12) [8]. The enol ethers used, i.e., ethyl vinyl

• good yields and stereoselectivities, 5 equivalents of the nucleophile were necessary to achieve reasonable yields in the addition to the nitrone/chlorodiethylaluminium complexes. Despite this, diastereomeric ratios in favour of the anti-products were generally excellent. Lithiated ethyl vinyl ether was

• also added to pre-complexed D-arabinose-derived nitrone 2c (Scheme 2). After a subsequent TBS-protection step, the desired hydroxylamine derivative anti-4e was obtained in low yield, but with excellent diastereoselectivity. Next, the protected hydroxylamine derivatives syn-4 and anti-4 were treated

Bioorthogonal metabolic glycoengineering of human larynx carcinoma (HEp-2) cells targeting sialic acid

• Arne Homann,
• Riaz-ul Qamar,
• Sevnur Serim,
• Petra Dersch and
• Jürgen Seibel

Beilstein J. Org. Chem. 2010, 6, No. 24, doi:10.3762/bjoc.6.24

• ), followed by N-acylation with the activated ester 7 led to the alkyne 8 in a yield of 75% based on D-arabinose. A [3+2] cycloaddition reaction between N-tert-butyl nitrone 9 and 8 and subsequent base-catalyzed ring-opening and hydrolysis afforded N-(1-oxohex-5-ynyl)neuraminic acid (Neu5Hex, 3) in 38% yield

• -butyl-5-(1”-(hex-5’-ynoyl)amino-2’’,3’’,4’’,5’’-tetrahydroxy-pentyl)-isoxazolidine-3-carboxylic acid ethyl ester Polyhydroxy olefin (1.50 g, 5.53 mmol, 8) and nitrone (2.01 g, 11.6 mmol, 9) in dioxane (100 mL) were stirred at 30 °C for 14 d. After complete conversion of the starting material as

The use of silicon- based tethers for the Pauson- Khand reaction

• Adrian P. Dobbs,
• Ian J. Miller and
• Saša Martinović

Beilstein J. Org. Chem. 2007, 3, No. 21, doi:10.1186/1860-5397-3-21

• explanation for the failure of all these reactions was that the 'arms' of the silyl ethers were too far apart for cyclisation to occur. We had already attempted to overcome this potential hurdle by the introduction of functionality within the side chains. Work by Denmark[25] on tethered nitrone cycloadditions