Applications of 1,3-dipolar cycloadditions

The application of 1,3-dipolar cycloaddition processes to the synthesis of substituted tetrahydrofurans has been investigated, starting from epoxides and alkenes under microwave irradiation. The epoxide 85 was rapidly converted into carbonyl ylide 86 that behaved as a 1,3-dipole toward various alkenes, leading to quantitative yields of tetrahydrofuran derivatives 87 (Scheme 30). The reactions were performed in toluene within 40 min instead of 40 h under classical conditions, without significantly altering the selectivi-ties [64]. 

A series of 3-substituted-2-isoxazoles are prepared by the following simple procedure in situ conversion of nitroalkane to the silyl nitronate is followed by 1,3-dipolar cycloaddition to produce the adduct, which undergoes thermal elimination during distillation to furnish the isoxazole (Eq. 8.74). 5 Isoxazoles are useful synthetic intermediates (discussed in the chapter on nitrile oxides Section 8.2.2). Furthermore, the nucleophilic addition to the C=N bond leads to new heterocyclic systems. For example, the addition of diallyl zinc to 5-aryl-4,5-dihydroi-soxazole occurs with high diastereoselectivity (Eq. 8.75).126 Numerous synthetic applications of 1,3-dipolar cycloaddition of nitronates are summarized in work by Torssell and coworker.63a... 

G. Mloston and H. Heimgartner, The chemistry of heterocyclic compounds, in Synthetic Application of 1,3-Dipolar Cycloaddition Chemistry toward Heterocyclic and Natural Products, A. Padwa, W.H. Pearson (eds), vol. 59, Wiley, New York, 2002. 

Jager F, Colinas PA. In Synthetic Applications of 1,3-Dipolar Cycloaddition Chemistry Toward Heterocycles and Natural Products, Padwa A, Pearson EH (Ed.), John Wiley Sons, New York, ch. 6, 361, 2002. 

Denmark SE, Cottell JJ. The Chemistry of Heterocyclic Compounds, Vol. 59 Synthetic Applications of 1,3-dipolar Cycloaddition Chemistry Toward Heterocycles andNatural Products , John Wiley Sons, pp 83-167, 2002. 

Martin JN, Jones RCE (2003) In Padwa A, Pearson WH (eds) Application of 1,3-dipolar cycloaddition chemistry towards heterocycles and natural products, chap 1. Wiley, Hoboken... 

SYNTHETIC APPLICATIONS OF 1,3-DIPOLAR CYCLOADDITION CHEMISTRY TOWARD HETEROCYCLES AND NATURAL PRODUCTS... 

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