Azides intermolecular cycloadditions

Closely related to the already mentioned electrocyclizations of N-acyl thione S-imide (see Section 4.14.9.2) are some intermolecular cycloadditions involving this unusual class of 1,3-dipoles. Thus, the thione-S-imide intermediate (233) is probably involved in the formation of spirodithiazoline derivative (234) from the thione (235) and aryl azides <93HCA2147>. Also fluorenone-S-/ -tosylimide affords with carbonyl or thiocarbonyl compounds (R H) the corresponding oxathia- or dithia-zolidine derivatives (236) (Y = O or S) <80BCJ1023> (Scheme 44) (see also Section 4.14.6.1). 

A synthesis of the 11-aryl-1 l-aza[5.3.1 ]propellan-2-one 29 was accomplished by the intermolecular cycloaddition of the cycloheptenone 26 with an aryl azide. The... 

Junjappa and co-workers (9) reported the cycloaddition of sodium azide to the polarized ketene-(5,5)-acetal 33 to give the tiiazole 35 they also reported an intermolecular cycloaddition of tosyl azide 37 with the enamine 36 to give an unstable triazoline intermediate 38. Ring opening 38 followed by a Dimroth rearrangement afforded the triazole 41 (Scheme 9.9). 

Kadaba (14) reported the first example of an intermolecular cycloaddition of sodium azide with a vinyl azide (60) to give the tetrazole 62 in 25% yield (Scheme 9.14). 

Hassner et al. (15) explored the synthetic utility of the polymeric azidation reagent 63 to prepare di- and tri-azidomethanes 64 and 66 at ambient temperature. They also studied the intermolecular cycloaddition of these azides with dimethyl acetylenedicarboxylate (DMAD) to yield the corresponding cycloadducts... 

Benati et al. (17) reported intermolecular cycloadditions of aryl azides with 1,4-naphthoquinone (72) at ambient temperature. The triazohne intermediate 73 was unstable even at room temperature, leading to the formation of a mixture of products 74—77 (Scheme 9.17). 

De Kimpe and Boeykens (22) reported synthesis of the p-lactam derivatives 107 via cycloaddition of azides with 2-methyleneazetidines (104) (Scheme 9.22). Because of electronic control, the intermolecular cycloaddition of the azide with the enamine double bond resulted in the formation of the triazoline intermediate 105, ring opening and rearrangement of which gave the imino lactam 107. Although all attempts to convert compound 107 to the corresponding p-lactam 108 under acidic conditions were unsuccessful, under basic conditions compound 107 was converted into the p-amino amides 109. 

The stereoselective intermolecular cycloaddition of azides to chiral cyclopenta-none enamines was reported, but both product yields and enantiomeric excesses (ee) were low (24) (Scheme 9.24). Ethyl azidoformate (115) and A-mesyl azido-formamimidate (116) underwent 1,3-dipolar cycloaddition with the monosubsti-tuted chiral enamine 114 to give products 117 and 118 in low yields with ee of 24 and 18%, respectively. Intermolecular cycloaddition of the A-mesyl azidoforma-mhnidate 116 with the disubstituted C2-symmetric chiral enamine 119 proceeded with good diastereoselectivity to give compound 120 in 18% yield. On cleavage of the enamine unit, compound 120 afforded 118 with low ee. 

Wedegaertner and Kattak (27) reported the intermolecular cycloaddition of aryl azides with allenes (Scheme 9.27). Cycloaddition of an aryl azide with the 1,2-propanediene 131 produced a mixmre of the isomeric triazolines 132 and 133, whereas when the cycloaddition was conducted with cyclonona-1,2-diene 134, the triazoline 135 was the sole product. X-ray crystallographic analysis confirmed the stmcture of 135. 

Clerici and co-workers (28) reported an intermolecular cycloaddition of azides with the isothiazole dioxides 136 to give the triazolines 137 further heating of cycloadduct 137, just above its melting point, resulted in the extmsion of nitrogen to give the aziridine 138 (Scheme 9.28). 

A general synthesis of functionalized 1,2,3-triazolyl acylsilanes (160) was based on the intermolecular cycloaddition of azides 159 with the alkynyl acylsilane 158 (Scheme 9.32) (32). The resulting triazolyl acylsilanes (160) were smoothly converted into their corresponding aldehydes 161 upon treatment with sodium hydroxide in ethanol. 

A remarkable intermolecular cycloaddition has been reported. The a-trisaccharide azide 263, obtained by the trimethylsilyl method and carrying a suitable propynyl function at C-4 " was treated under CuI-DBU-catalyzed cyclization conditions. The cyclodextrin-resembling cyclodimer 264 was obtained as the main product in 80% yield, hydrogenolysis of which gave the water-soluble cyclodextrin analog 265. The formation of a corresponding cyclotrimer in 15% yield was also observed. 

If the substrate contains both azide and alkyne functional groups, intramolecular and intermolecular cycloaddition reactions are possible. While the former... 

Apart from the utilization of aryl- and vinyl-diazoacetates that can achieve the moderate to high chemo-, regio-, and enantioselectivity in intermolecular asymmetric C—H bond insertion reactions, Af-sulfonyl-l,2,3-triazole 11 was found to be able to function as an alternative carbene precursor for diverse transformations (Scheme 1.4). One advantage for using the N-sulfonyl-1,2,3-triazole is that it could be easily prepared by the Cu -catalyzed azide-alkyne cycloaddition (CuAAC) reaction, and in some cases, delicately designed reactions can be conducted in a one-pot procedure starting from alkynes and sulfonyl azides. Moreover, since there exists an inherent equilibrium... 

Figure 9.16 Stereoeiectronic basis for assistance to bond formation provided by acceptors in azide-aikyne cycloadditions. This example Illustrates how Intermolecular transfer of electron density and stereoeiectronic effects can amplify each other.

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