Cycloaddition reaction experimental procedure

Cyclizations proceeding by nucleophilic attack at noncarbonyl centers Free radical cyclizations Cycloaddition reactions Experimental Procedures... 

Although it was stated that allyltrialkylsilanes were unsuccessful in the Lewis acid mediated addition to acryloylFp complexes, a stereoselective procedure has been developed for [3 + 2] cycloadditions of allylsilanes to enones10. The reaction occurs in the presence of titanium(IV) chloride (TiCl4) as Lewis acid and the single cycloaddition product formed is the m-fused eyclopentane with the trimethylsilyl group in the endo orientation. The reaction appears to follow a similar pathway to the previous process although, as yet, yields and experimental procedures have not been documented. 

The hetero Diels-Alder reaction <01H1591, 01TL5693> and dipolar cycloadditions continue to constitute important approaches to piperidines. Kibayashi and co-workers used an intramolecular acylnitroso Diels-Alder reaction to synthesize (-)-lepadins A,B, and C from an acyclic precursor <01JOC3338>. An intramolecular nitrone cycloaddition was used by Machetti and co-workers to produce both enantiomers of 4-oxopipecolic acid <01T4995>. Their synthesis proceeds from a nitrone bearing an a-methylbenzylamine chiral auxiliary. Noteworthy in this report is the presence of large-scale experimental procedures the nitrone formation and cycloaddition reactions were performed on 285 mmol and 226 mmol scales, respectively. 

No experimental procedure is given for this reaction. Other references related to [3+2+2+2] cycloaddition are cited in the literature. ... 

Experimental procedure for the [4+2] cycloaddition of N-snlfinyl dienophile 166 A solution of thionyl chloride in CH2CI2 (3.2mL, 2M, 6.4 mmol) was added via a syringe pump over 2.5 hours to a stirred solution of diene urea 165 (1.82g, 3.1 mmol) and imidazole (0.85 g, 12.5 mmol) in CH2CI2 (75 mL) at —78°C. Once the addition was complete, the reaction mixture was stirred for a further 2 hours at —78°C and then slowly allowed to warm to room temperature over 14 hours. The mixture was then filtered, and the filtrate was concentrated in vacuo to afford dark hrown oil. Purification of this residue hy flash chromatography... 

In 2013, Ayoob Bazgir et al. reported 1,1,3,3-tetramethylguanidine (TMG)-catalyzed synthesis of 1,2,3-triazoles via the cycloaddition reaction of azides and CH acids 22 in ethanol at 30 °C, employing simple experimental procedure, short reaction times, mild reaction conditions to provide good yields (Scheme 4.21) [25]. In the actual procedure, a mixture of CH acid 22 (1 mmol), azide 2 (1 mmol), and TMG (15 mol%) in EtOH (5 ml) was stirred for an appropriate time at 30 C. After completion, the solvent was removed under reduced pressure and the residue was washed with ether (5 ml) and re crystallized from CHClj/w-hexane (1 3) to afford the pure products 64. A wide diversity of CH acids 22 and aryl azides 2 were acceptable for this reaction. The reaction of cyclic 1,3-diketones 65 with aryl azides 2 generated the bicyclic or tricyclic triazoles 66 in good isolated yields. 

On the other hand, using cyclopropyl-substituted allylic trifluoroacetate 12 led to [5 + 2] cycloaddition product 13 after the temperature was raised to 80 °C (Scheme 8). Both procedures are experimentally simple since only a change in temperature is necessary to promote the second step of the sequential reactions. 

In an Initio study of the tautomerism of 2- and -hydroxy-pyridines, 4 -hydroxypyridine was calculated to be 2.4 kcal/mol more stable than 4-pyridone. 2-Pyridone was calculated to be 0.3 kcal /mol more stable than 2-hydroxypyridine and this is in good agreement with experimental values obtained from tautomeric studies in the gas phase.A study of the bromination of the 2-pyridone/2-hydroxypyridine system has revealed that reaction occurs via the principal "one" tautomer at pH<6 and via the conjugate anion at pH>6. Attack on the "one" occurs preferentially at the 3-position, whereas on the anion it probably occurs mainly at the 5-position. The facile formation of 3f5-dibromo-2-pyridone results from the comparable reactivity of the monobromopyridones at pH<1 and pH>4- Practical procedures have been reported for the preparation of 3-bromo-2-pyridone and 3,5-dibromo-2-pyridone Cycloaddition of 2-substituted pyridinium betaines with unsymmetrical alkenes gives products of mixed orientation for example, treatment of (40) with methyl... 

---