Cycloadditions ethoxy acetylene

Norbornadienes, norbornenones and their homologs have been prepared [23, 24] by cycloaddition of cyclopentadiene (21) and cyclohexadiene (22) with l-benzenesulfonyl-2-trimethylsilylacetylene (23) and l-ethoxy-2-carbomethox-yacetylene (24). Both were efficient dienophiles in the cycloaddition processes and dienophile 23 acted as an effective acetylene equivalent (Scheme 2.12). Norbornanes and their homologs can also be attained by Diels-Alder reaction... 

Beccalli et al. reported a synthesis of carbazomycin B (261) by a Diels-Alder cycloaddition using the 3-vinylindole 831 as diene, analogous to Pindur s synthesis of 4-deoxycarbazomycin B (619). The required 3-vinylindole, (Z)-ethyl 3-[(l-ethoxy-carbonyloxy-2-methoxy)ethenyl]-2-(ethoxy-carbonyloxy)indole-l-carboxylate (831), was synthesized starting from indol-2(3H)one (830) (620). The Diels-Alder reaction of the diene 831 with dimethyl acetylene dicarboxylate (DMAD) (535) gave the tetrasubstituted carbazole 832. Compound 832 was transformed to the acid 833 by alkaline hydrolysis. Finally, reduction of 833 with Red-Al afforded carbazomycin B (261) (621) (Scheme 5.99). 

The thermal or photolytic decomposition of carbonyl azides in the presence of dipole acceptors such as acetylenes provides a valuable method for the construction of oxazoles. Thus the reaction of ethyl azidoformate with either diphenyl- or diethylacetylene produces mainly the 2-ethoxy-oxazole (77 ).166 166 The reaction involves the 1,3-dipolar cycloaddition of carbethoxy nitrene (76b) to the alkyne to give the oxazole (77). On the... 

Ethoxy(trimethylsilyl)acetylene reacted by a [2 + 2 + 2] cycloaddition with diyne 11 in the presence of 10 mol% Rh(cod)2-BF4 and 10 mol% rac-BlNAP in dichloromethane (0.021 M) at ambient temperature to give aryl ether derivative 12 in 50% yield, thus providing a valuable synthetic route to highly substituted benzene derivatives (eq 9). ... 

The readily available and inexpensive CU2O seems to be quite robust and catalyzes aqueous azide-alkyne cycloaddition reactions efficiently, even with very low loadings (ppm levels). A range of functional groups on the acetylene including halo-, cyclopropyl-, ethoxy-, amide, ether, and double bonds were well... 

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