The enantiospecific synthesis of (+)-monomorine I using a 5-endo- trig cyclisation strategy

• Malcolm B. Berry,
• Donald Craig,
• Philip S. Jones and
• Gareth J. Rowlands

Beilstein J. Org. Chem. 2007, 3, No. 39, doi:10.1186/1860-5397-3-39

• epimer, with the methyl group residing in the axial position. Naturally, we had assumed that the diastereoisomer in which all the substituents adopted a pseudo-equatorial orientation would have been formed preferentially. Yet inspection of the possible transition states for the cyclisation 25 vs. 27

Electronic differentiation competes with transition state sensitivity in palladium- catalyzed allylic substitutions

• Dominik A. Lange and
• Bernd Goldfuss

Beilstein J. Org. Chem. 2007, 3, No. 36, doi:10.1186/1860-5397-3-36

• distances (Å) of transition states and Pd-ene product complexes (pb = phosphabenzene; py = pyridine)[a] Acknowledgements We are grateful to the Fonds der Chemischen Industrie for financial support as well as for a Dozenten-Stipendium to B.G. We especially thank the Deutsche Forschungsgemeinschaft (DFG) for

Conformational rigidity of silicon- stereogenic silanes in asymmetric catalysis: A comparative study

• Sebastian Rendler and
• Martin Oestreich

Beilstein J. Org. Chem. 2007, 3, No. 9, doi:10.1186/1860-5397-3-9

• enantiomer of 4 is preferentially funnelled out via diastereomeric transition states (11 → 12). There is one major difference between the diastereoselectivity-determining steps in these catalytic cycles: (ii) in Scheme 3 and (iv) in Scheme 4. In the migratory insertion (ii, 7 → 8), carbon-silicon bond

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

• asymmetric induction is strong intermolecular interactions like electrostatic attraction and hydrogen bonding between ionic solvents and intermediates or transition states of the diastereoselective reaction step (Figure 1). This observation was made by our group[25] and further confirmed by Leitner and co

Trapping evidence for the thermal cyclization of di-(o-acetylphenyl)acetylene to 3,3'-dimethyl- 1,1'-biisobenzofuran

• Charles P. Casey,
• Neil A. Strotman and
• Ilia A. Guzei

Beilstein J. Org. Chem. 2005, 1, No. 18, doi:10.1186/1860-5397-1-18

• to alk-2-en-4-yn-1-ones (Scheme 10). These ring openings have been studied both experimentally by matrix isolation spectroscopy [22][23] and computationally [24][25] and are described as involving coarctate transition states.[26] The transformation of 1 to A can be viewed as a coarctate ring closure

High stereoselectivity on low temperature Diels- Alder reactions

• Luiz Carlos da Silva Filho,
• Valdemar Lacerda Júnior,
• Mauricio Gomes Constantino,
• Gil Valdo José da Silva and
• Paulo Roberto Invernize

Beilstein J. Org. Chem. 2005, 1, No. 14, doi:10.1186/1860-5397-1-14

• product. This would increase the usual difference between the two transition states, normally due mainly to π orbital overlaps. As already mentioned, we are performing HOMO-LUMO and transition states calculations to verify some structural factors influences on the course of these reactions. Conclusion

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

• as the co-ordinating auxiliary appear to play a role in influencing the high diastereoselectivity observed for products 24 and 25. The reaction presumably progresses via a six-membered transition-state as depicted in Scheme 6. There are two possible disastereoisomeric transition states with either

• 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

Synthesis and glycosidase inhibitory activity of new hexa- substituted C8-glycomimetics

• Olivia Andriuzzi,
• Christine Gravier-Pelletier,
• Gildas Bertho,
• Thierry Prangé and
• Yves Le Merrer

Beilstein J. Org. Chem. 2005, 1, No. 12, doi:10.1186/1860-5397-1-12

• protonated, and the corresponding ammonium ions mimick the charge of the presumed transition states or intermediates of the enzymatic glycoside hydrolyses [18]. More recently, attention has been increasingly accorded to seven- and eight-membered ring systems [19][20][21][22][23][24][25][26][27][28][29][30