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33.4.14.1.1 Method 1: Condensation of Arylaldehydes with α-Azido-Esters

DOI: 10.1055/sos-SD-033-00606

Collier, S. J.Science of Synthesis, (200733544.

By far the most widely used approach to alkenyl azides is the base-mediated condensation between aldehydes (usually aryl- or hetarylaldehydes) and α-azidocarbonyl compounds. Many examples of such reactions involve the condensation of azidoacetate esters, e.g. 12, with aldehydes, e.g. 11, which give azidocinnamate esters, e.g. 13, and a range of these are given in Scheme 4. Many other examples are not discussed in detail, but are referenced here should further information be required. Most commonly these reactions are performed using alkoxide bases in alcohols at low temperatures. In the vast majority of cases, the resulting product has the azide unit and the aryl group cis to one another; however, some cases report formation of E/Z mixtures of isomers.[‌27‌,‌48‌] The two-step sequence of condensation of an azido ester with a benzaldehyde, followed by thermal cyclization to give an indole-2-carboxylic acid ester is sometimes known as the HemetsbergerKnittel reaction.[‌51‌,‌129‌‌131‌] With sterically hindered aldehydes, the condensation can be difficult, but use of a large excess of the diazo ester can facilitate the reaction. It has also been noted that methyl and ethyl azidoacetate are not particularly stable to the basic reaction conditions. Use of tert-butyl azidoacetate can provide improved yields in these reactions,[‌51‌] but usually use of a large excess of the methyl or ethyl azidoacetate is employed. When the reaction is run at low temperatures, dehydration of the intermediate azido alcohol may not take place to allow isolation. Subsequent treatment with dehydrating agents effects formation of the required alkenyl azide, and this approach is considered in Section 33.4.14.1.2.[‌27‌,‌51‌] Running the reaction at a slightly higher temperature usually allows condensation and dehydration in the same reaction,[‌27‌] although in the case of some N-unsubstituted carbazole aldehydes, the condensation gives only the azido alcohol, and attempted dehydrations to give the alkenyl azide have failed.[‌66‌]

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Meeeee 8 Meeeeeeeeeeeee Meeeeeeeeee eeee eee Meeeeeee ee Meee Meeeeeeee eeee Meeeeeeeeeeee[‌88‌,‌88‌,‌88‌,‌88‌,‌88‌,‌88‌,‌88‌,‌88‌,‌88‌,‌88‌,‌88‌,‌88‌,‌88‌,‌888‌,‌888‌,‌888‌,‌888‌,‌888‌,‌888‌,‌888‌]

Meeeeeeeeee 8

Me8 M8 Meeeeeeeee Meeee (%) Mee
Me MeMMe, MeMM, 88°M, 8.8e 88 [‌88‌]
Me MeMMe, MeMM, 88°M, 8e 88 [‌888‌]
Me MeMMe, MeMM, 88°M, 8e 88 [‌888‌]
Me MeMMe, MeMM, 8°M, 8e 88 [‌88‌]
Me MeMMe, MeMM, 88°M 88 [‌88‌]
Me MeMMe, MeMM, MMM, 88°M 88 [‌88‌]
Me MeMMe, MMM, 88 ee 8°M, 8e 88 [‌88‌]
Me MeMMe, MeMM, 88°M 88 [‌888‌]
Me MeMMe, MeMM, 88°M, 8e 88 [‌88‌]
Me MeMMe, MeMM, 88°M 88 [‌888‌]
Me MeMMe, MeMM, 88°M 88 [‌888‌]
Me MeMMe, MeMM, 888°M, 88eee 88 [‌88‌]
Me MeMMe, MeMM, 888°M, 8e 88 [‌88‌]
Me MeMMe, MeMM, 88°M 88 [‌88‌]
Me MeMMe, MeMM, 88 ee 8°M, 8.88e 88e [‌888‌]
Me e-MeMM, e-MeMM, MeMM, 88 ee 88°M, 8e 88 [‌88‌]
Me MeMMe, MeMM, 88°M, 8.8e 88e [‌88‌]
Me MeMMe, MeMM, eeeeeeee, 8 ee 8°M, eeee 8°M, eeee ee 88 [‌88‌]
Me MeMMe, MeMM, 88°M 88e [‌888‌]
Me MeMMe, MeMM, 8°M, 8e, eeee 8°M, 88e 88 [‌88‌]

e Meeee eeeee.

e Meeee ee eeeeeee.

e Meeee ee eeeeeee. M eeeee ee 88% eee eee eeeeeeeee eee eeee eeeeeeee.

Meeeeeee ee eeee eeeee eeee- eee eeeeeeeeeeeeeeee eee eeee ee eeeee eeeeeeeeeeeeeee, eeeee eeeeeeeee eee ee eeee (Meeee 8). Meeeeeeeeeeeee eeeeeeeeeee eeeeeeee eeee eeeee eeeeee (eeeeeee 88)[‌888‌‌888‌] eee eeeeeee eeeeeeeeeeeee ee eee eeeeeeeee eeeeeee eeeeee eeeeeeee eeeee 8-eeee-8M-eeeeeee-8-eeeeeeeeeeee. Meeeeeeeeeee eeeeeeeee ee eeeeeeeeeeeeee eee eeee ee eeee (eeeee 8),[‌888‌] eee, ee eeee eeee, eeeeeeeeeee eeeee eeee ee 8,8-eeeeeeeeee. Meeeeeeeeeeeeee eeeeeeeee eee ee eeee (eeeee 8),[‌888‌] eeeeee eeeeeee-8-eeeeee eeeee eeeeeeeeee ee eee eeeeeeeee eeeeeee eeeee eeee ee eeeeeeeeeeeeeeee eee eeeeeeeee eeee eeeeeeeeeee. α-Meeee eeeeeee eee eeee ee eeee ee eeeeeeeeeeee eeeeeeeee eeee eeeeeeeee;[‌888‌,‌888‌‌888‌] ee eeee eeee, eee eeeeeeeee eee eeeee eeeeeeee ee eeeeeeeeeeee eeeeeee, eeeeee eeee ee eeeeeeee eeee, eeeeee eee eeeeeeeeeeeee eeeeeee eeeeeee. Mee eee ee eeeeeeeee eeeeeeeee eee eeee eeee eeeeeeee, eee eeeee eeeeeeee eee eeee.[‌88‌,‌888‌,‌888‌,‌888‌,‌888‌]

Meeee 8 Meeeeeeeeeeee ee Meeeeeeee eeee Meeeeeeeeeeee Meeeeeeee[‌88‌,‌888‌,‌888‌,‌888‌‌888‌,‌888‌]

Meeee M8 M8 Meeeeeeeee Meeee (%) Mee
8 MMe MeMMe, MeMM, 88°M ee ee, 8.8e 88 [‌888‌]
8 MMe MeMMe, MeMM, 88°M ee ee, 8.8e 88 [‌888‌]
8 MMe MeMMe, MeMM 888 [‌888‌]
8 MMe MeMMe, MeMM, 88 ee 8°M, 8e 88e [‌888‌]
8 MMe MeMMe, MeMM, 88°M, 8e 88 [‌888‌]
8 8-MeMM8M8 eeeeeeeeeeee eeeeeee, MeMM, ee, 88e 88 [‌888‌]
8 Me eeeeeeeeeeee eeeeeee, MeMM, ee, 88e 88 [‌888‌]
8 8-MeMM8M8 8-Mee eeeeeeeeeeee eeeeeee, MeMM, 8888e 88 [‌888‌]
8 Mee 8-MeM8M8 eeeeeeeeeeee eeeeeee, MeMM, 8888e 88 [‌888‌]
88 8-M8MM8M8 8-MeM8M8 eeeeeeeeeeee eeeeeee, MeMM, 8888e 88 [‌888‌]
88 8,8-Me8M8M8 8-MeM8M8 eeeeeeeeeeee eeeeeee, MeMM, 8888e 88 [‌888‌]
88 Me 8-MeM8M8 eeeeeeeeeeee eeeeeee, MeMM, ee, 88e 88 [‌888‌]
88 Me 8-MeM8M8 eeeeeeeeeeee eeeeeee, MeMM, ee, 88e 88 [‌888‌]
88 8-MeM8M8 eeeeeeeeeeee eeeeeee, MeMM e [‌88‌]

e Meeee eeeeeeeeeee.

e Mee eeeeeeee.

Meeeee 8 eeeeeeeeeee eeee eeeeeeee eeeeeeeee ee eeeeeee eeeeeeeee 88 eeee eeeee eeeeeeeeeeee ee eeee eee eeeeeeeeeeeeeee 88.[‌88‌]

Meeeee 8 Meeeeeee ee Meeeeeeee eeee Meeee Meeeeeeeeeee[‌88‌]

Meeeeeeeeee 8

Me8 Meeee (%) Mee
8-eMeM8M8 88 [‌88‌]
8-Mee 8888 [‌88‌]
Mee 88 [‌88‌]
8-MeM8M8 8888 [‌88‌]
8-MeMM8M8 88 [‌88‌]
8,8-Me8M8M8 88 [‌88‌]
88 [‌88‌]
88 [‌88‌]
88 [‌88‌]

Meeeeeeeeeee Meeeeeeee:

Meeeeeeeeeeeeee 88; Meeeeee Meeeeeeee:[‌88‌]

Me (8.88e, 8.88eee) eee eeeeeeeee ee MeMM (88eM) eee eee eeee eee eeeeee ee 88°M. M eeeeeee ee eee eeeeeeee 88 (8.88eee) eee eeeee eeeeeeeeeeee (88.88e, 8.88eee) eee eeeee eeeeeeee eeee eeeeeeee ee e eeee eeee eeeeeeeeee eee eeeeeeeeeee eeeee 88°M. Me eee eeeeeeee eee eeeeeeeee ee eeeee eeeeeeeeeeee, eeeeeeeeee MeMM ee MMM eee eeeee ee eeeeeee eeeeeeee eeeeeeeeeee. Mee eeeeeee eee eeeeeee ee ee. 88°M eeeee MMM eeeeeeee eeeeeeeee eeee eee ee eee eeeeeeee eee eeee eeeeeeee (88e), eee eee eeeeeee eee eeee eeeeeee ee eeee ee ee. Mee eeeeeee eee eeeeee eeee eee eeeee eee eeeeeeeee eeee Me8M (8×888eM). Mee eeeeeeee Me8M eeeeeeee eeee eeeeee eeee M8M, eeeee, eee eeeeeeeeeeee eeeee eeeeeee eeeeeeee ee eeee eee eeeee eeeee, eeeee eee eeeeeeee ee eeeeee eeeeeeeeeeeeee eee eeeeeeeeeeeeeeeee ee eeeee; eeeee: 8888%. Meeee eeeeeee eeeeeeeee eeee eeee eeeeeeeee eeeee 88 eeeee ee eee eeeeeeeeeeee ee eeeeeeee eee eeeeeeee eeeeee.

References


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