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

• , even after prolonged reaction times. The reactions with stoichiometric amounts of TMSOTf gave monocyclic, bicyclic, and spirocyclic dihydropyrans depending on the 1,3-dioxolanyl-substituted enol ether employed (Table 2). Unfortunately, attempts to generate an eight-membered (or six-membered) ring by

Synthesis of spiroannulated and 3-arylated 1,2,4-trioxanes from mesitylol and methyl 4-hydroxytiglate by photooxygenation and peroxyacetalization

• Axel G. Griesbeck,
• Lars-Oliver Höinck and
• Jörg M. Neudörfl

Beilstein J. Org. Chem. 2010, 6, No. 61, doi:10.3762/bjoc.6.61

• nitro-substituted compound 10e as the most active derivative (EC50 = 48 μM) [25]. Thus, the peroxide bond lengths do not correlate with biological activity, cf. the highly active AM and the fluoro compound 10b. Conclusion In summary, we have reported the synthesis of a series of six-membered ring 3,3

Synthesis of a new class of aminocyclitol analogues with the conduramine D-2 configuration

• Latif Kelebekli,
• Yunus Kara and
• Murat Celik

Beilstein J. Org. Chem. 2010, 6, No. 15, doi:10.3762/bjoc.6.15

• groups in aminocyclitol 18 [25] attached to the six-membered ring resembles the configuration of conduramine D-2 [36][37][38]. Hydrolysis of the acetate groups with H2SO4 proceeded smoothly to deliver aminocyclitol 6 in 84% yield. For the synthesis of dichloro derivative, we replaced the acetoxy groups

• between H1, H2, H3 and H4 protons. We assume that the stereochemical course of the hydroxylation of 27 proceeds through syn addition as previously observed in the hydroxylation of 13, a quite similar structure to 27. The all cis-configuration of the acetate and amino groups attached to the six-membered

• ring resembles the configuration of conduramine D-2 [31][40][41]. The cyclic polyhdroxylated amines, also known as aminocyclitols, possess a wide variety of biological activities [42][43][44][45]. In conclusion, we have outlined the synthesis of a new family of aminocyclitols analogues 6 and 7 based on

Pd/C-mediated synthesis of α-pyrone fused with a five-membered nitrogen heteroaryl ring: A new route to pyrano[4,3-c]pyrazol-4(1H)-ones

• Dhilli Rao Gorja,
• Venkateswara Rao Batchu,
• Ashok Ettam and
• Manojit Pal

Beilstein J. Org. Chem. 2009, 5, No. 64, doi:10.3762/bjoc.5.64

• pyrazole ring, e.g. pyrano[4,3-c]pyrazol-4(1H)-one B (Figure 1). Synthesis of compound B could be achieved by either of the following strategies: construction of the six-membered ring followed by five-membered one or vice versa. However, only one method has been reported so far that falls to the first

2-Phenyl- tetrahydropyrimidine- 4(1H)-ones – cyclic benzaldehyde aminals as precursors for functionalised β²-amino acids

• Markus Nahrwold,
• Arvydas Stončius,
• Anna Penner,
• Beate Neumann,
• Hans-Georg Stammler and
• Norbert Sewald

Beilstein J. Org. Chem. 2009, 5, No. 43, doi:10.3762/bjoc.5.43

• acyclic resonance stabilised Schiff bases are preferentially formed. Consequently, one pot cyclisation protocols employing conditions such as KOH in protic solvents deliver the desired six-membered ring only in unsatisfactory yields [30][39]. An alternative approach to cyclise benzaldehyde-derived imines

Radical carbonylations using a continuous microflow system

• Takahide Fukuyama,
• Md. Taifur Rahman,
• Naoya Kamata and
• Ilhyong Ryu

Beilstein J. Org. Chem. 2009, 5, No. 34, doi:10.3762/bjoc.5.34

• able to obtain the desired six-membered ring lactam 8 in good yield (entry 4). Using a similar microflow system, we then carried out a three-component coupling reaction comprised of 1-iodooctane (9), CO, and methyl vinyl ketone in the presence of tributyltin hydride [24], which also worked well to give

Analogues of amphibian alkaloids: total synthesis of (5R,8S,8aS)-(−)-8-methyl- 5-pentyloctahydroindolizine (8-epi-indolizidine 209B) and [(1S,4R,9aS)-(−)-4-pentyloctahydro- 2H-quinolizin- 1-yl]methanol

• Joseph P. Michael,
• Claudia Accone,
• Charles B. de Koning and
• Christiaan W. van der Westhuyzen

Beilstein J. Org. Chem. 2008, 4, No. 5, doi:10.1186/1860-5397-4-5

• expected to produce not only a cis-relationship between C-1 and C-9a, but also a cis-relationship between C-4 and C-9a. The developing chair conformation of the six-membered ring in the transition state should result in an equatorial preference for the pentyl side chain, which in turn should bias the

Asymmetric aza-Diels- Alder reaction of Danishefsky's diene with imines in a chiral reaction medium

• Bruce Pégot,
• Olivier Nguyen Van Buu,
• Didier Gori and
• Giang Vo-Thanh

Beilstein J. Org. Chem. 2006, 2, No. 18, doi:10.1186/1860-5397-2-18

• efficiency is preserved. Background Aza-Diels-Alder reactions rank among the most efficient method for the construction of nitrogen-containing six-membered ring compounds.[1] The reaction of Danishefsky's diene 1 with imine 2 provides a convenient protocol for the synthesis of 2-substituted-2,3-dihydro-4

Investigation of acetyl migrations in furanosides

• O. P. Chevallier and
• M. E. Migaud

Beilstein J. Org. Chem. 2006, 2, No. 14, doi:10.1186/1860-5397-2-14

• trans-esterification occurrence. Unfortunately, the formation of a six-membered ring orthoacetate appears to be facilitated under acid-catalysed reaction conditions and total intramolecular acetyl migration occurred in xyloside 2 in the presence of CAN, showing how finally balanced things are in these

• reaction conditions which could minimise the readily occurring intramolecular migration resulting from the formation of a five or six membered ring orthoacetate intermediate. Under such circumstances, migration can only be circumvented by controlling the stereochemistry of the reactive centres and opting

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

• with the addition of enone 2a to a clear solution. After completion and usual work-up, the product 3a was obtained in 85% yield. The reaction did not indicate the formation of any six-membered ring product pyrimido [4,5-c]pyridazine 5 as expected via [4+2] cycloadditions, which would have occurred

Stereoselective α-fluoroamide and α-fluoro- γ-lactone synthesis by an asymmetric zwitterionic aza-Claisen rearrangement

• Kenny Tenza,
• Julian S. Northen,
• David O'Hagan and
• Alexandra M. Z. Slawin

Beilstein J. Org. Chem. 2005, 1, No. 13, doi:10.1186/1860-5397-1-13

• the allyl group 'anti' (TS-A and TS-A') or 'syn' (TS-B or TS-B') with respect to the methyl ether substituent of the auxiliary. Models indicate that the B-transition states are much more relaxed than the A-transition states, with the transient six membered ring perpendicular to the fused five and