The first organocatalytic carbonyl- ene reaction: isomerisation- free C-C bond formations catalysed by H-bonding thio- ureas

• Matthew L. Clarke,
• Charlotte E. S. Jones and
• Marcia B. France

Beilstein J. Org. Chem. 2007, 3, No. 24, doi:10.1186/1860-5397-3-24

• reactions is severely limited. A step change in catalytic performance is required for this reaction to truly reach its potential. It remains to be seen whether the more entropically favoured intramolecular carbonyl ene cyclisation reaction holds more promise. In summary, we have developed the first

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

• . Saigo reported that the attempted P-K cyclisation of a variety of 3-sila-1,7-enynes underwent cycloisomerisation instead of the cycloaddition (Scheme 1).[7] Saigo's work showed that this cycloisomersiation was only applicable to 3-sila-1,7-enynes and any other chain length would undergo decomposition

• . Pagenkopf has shown that when the P-K cyclisation is carried out in 'wet' acetonitrile the cyclisation would proceed to give the cyclopentenones (Scheme 2).[8][9] The tethering strategy was not however successful in that although cyclisation gave the correct regiochemistry, the silicon tether is cleaved

• ] It can be seen that although the silicon methodology has been applied to the P-K reaction no group has been able to combine the synthetic diversity of silicon tethers with the synthetic benefits of the dicobalt octacarbonyl mediated cyclisation of alkynes and alkenes. Results and Discussion We

Novel base catalysed rearrangement of sultone oximes to 1,2-benzisoxazole- 3-methane sulfonate derivatives

• Veera Reddy Arava,
• Udaya Bhaskara Rao Siripalli,
• Vaishali Nadkarni and
• Rajendiran Chinnapillai

Beilstein J. Org. Chem. 2007, 3, No. 20, doi:10.1186/1860-5397-3-20

• )-one-2,2-dioxide Y = H), an obvious precursor for 5, was reported by Timoney et al., in an overall yield of ~30% [1] via the cyclisation of the methanesulfonate of salicylaldehyde followed by oxidation (Scheme 4). Results and discussion In order to prepare 6 in better yield, we choose methyl salicylate

• as the starting material and reacted it with methanesulfonyl chloride to provide the methanesulfonate derivative 9. After exploring different reaction conditions with NaOH and KOH as bases, it was found that NaH in DMSO was optimal for the cyclisation. Other strong bases also gave good yields of 6

Pd-catalysed [3 + 3] annelations in the stereoselective synthesis of indolizidines

• Olivier Y. Provoost,
• Andrew J. Hazelwood and
• Joseph P. A. Harrity

Beilstein J. Org. Chem. 2007, 3, No. 8, doi:10.1186/1860-5397-3-8

• the absence of the alkyllithium reagent. As outlined in Table 1, Entries 2–4, the annelation was found to proceed in the absence of n-BuLi, however, in all cases the yield of cyclisation product was significantly lower than with catalyst generated by the organolithium reagent. Whilst the underlying

• cyclisation onto the ester. Previous work in the quinolizidine area had shown that these transformations could be achieved in one-pot by the use of Mg turnings in methanol at ambient temperature [7][8]. Indeed, subjecting 10 to these conditions provided the desired indolizidine 11, albeit in modest yield

Tether- directed synthesis of highly substituted oxasilacycles via an intramolecular allylation employing allylsilanes

• Peter J. Jervis and
• Liam R. Cox

Beilstein J. Org. Chem. 2007, 3, No. 6, doi:10.1186/1860-5397-3-6

• interactions in the T.S. The 1,4-stereoinduction in these substrates is modest and seems to be modulated by the R substituent in the starting material. In the case of the syn-substrates, cyclisation through a chair T.S. is unlikely as this would require the methyl substituent α to the reacting carbonyl group

• stereoselective allylation of aldehydes (Scheme 2). [3] In this study, Lewis acid-mediated allylation of aldehyde 1, provided the oxasilacycle allylation products 2 and 3 in good yield. More significantly, owing to the complete 1,3-stereoinduction that is observed in this cyclisation, only these two – out of a

• large R groups in the cyclisation precursor 1, such as phenyl and cyclohexyl substituents, would serve as the most effective conformational anchors for our proposed chair-like T.S. (A values:[17] cyclohexyl: 2.2 kcal mol-1; phenyl: 2.8 kcal mol-1). These groups should occupy a pseudoequatorial position

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

• cyclic imide system. Thus no C=O group (other than the cyclic imide system) was indicated either from IR or 13C NMR spectrum. The 1H NMR spectra showed the absence of C-5 proton of the uracil moiety which supported the involvement of a cyclisation process. The absence of NH/OH group could be explained

• synthetic scope this reaction, we reacted 1,3-dimethyl-6-hydrazinouracil 1 with an α-ketoalkyne (3-hexyn-2-one) in refluxing ethanol, the reaction proceeded somewhat differently from that with an enone (Scheme 2), as the intermediate could undergo a 5-exo-trig cyclisation in preference to 7-exo-trig. Here

• in any strong acid. Here the reaction proceeded initially by the Michael addition of α-ketoalkyne 8 to 1 followed by cyclisation to a 5-membered ring (Scheme 4). Conclusion In conclusion, our results demonstrate a simple, mild and efficient method for the synthesis of novel functionalised pyrimido

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

• preference (10:1) for the anti diastereoisomer 20 as confirmed by 1H-NMR nOe analysis (Scheme 5). Iodolactonisation of diastereoisomer 19 again generated a single product (3S, 5R)-20, indicating a much more stereoselective cyclisation. In order to improve the stereoselectivity of the aza-Claisen