Substituted alkoxyacetylenes

The use of substituted alkoxyacetylenes in synthesis is fairly limited due to the lack of simple, general methods for their preparation. However, silyloxyacetylenes are easier to make and can be prepared from esters in a one-pot operation. In the laboratory of C.J. Kowalski, research has shown that silyloxyacetylenes could be successfully used in the Danheiser benzannuiation. This modification was used in the total synthesis of A-6-tetrahydrocannabinol. 

A similar approach has been employed in the syntheses of silicon, germanium, tin and boron " substituted alkoxyacetylenes. 

The bispyridine-substituted carbyne complexes 182 react with several anionic bidentate donor ligands to afford the anionic / -ketenyl complexes 183 [Eq. (149)] (149,167). The bis(pyrrole carboxaldiminato) complexes were further transformed into alkoxyacetylene complexes by methylation at the ketenyl oxygen atom. Addition of trimethylphosphine to the anionic carborane-substituted carbyne complex 184 at — 30°C gives the ketenyl complex 185 [Eq. (150)] (135). The hydroxy and methoxyacetylene complexes were obtained by further addition of HBF4 and methyl triflate. 

Wasserman and Clagett effected the synthesis of 1-substituted cyclopropanols starting with a 1-alkoxyvinyl ester (2) derivable from an alkoxyacetylene (1). In the... 

Danheiser and coworkers have developed a convenient synthetic approach to useful, highly substituted, aromatic compounds by the reaction of alkoxyacetylenes with cyclobutenone derivatives (equation 61) . The mechanism of this annulation is similar to the analogous reaction of siloxyacetylenes (equation 31, Section II.D.2) and the key step is a [2+2] cycloaddition of alkoxyacetylene with a vinylketene intermediate. ... 

Nucleophilic substitution at acetylenic C-atoms Alkoxyacetylenes from acetylenehalides... 

Allylboranes react with monosubstituted acetylenes and protonolysis of the resulting vinylboranes is a general method for synthesis of 1,4-substituted pentadienes (122). Using alkoxyacetylenes (R = OAIk) theresultingalkoxy-pentadienes can be hydrolysed to the non-conjugated enones. 

---