Alkoxyacetylenes

The first /3 -lactam was produced by addition of a ketene to an imine and there are now many examples of this type of approach. The ketenes are most frequently generated in situ from acid chlorides by dehydrohalogenation, but have also been produced from diazo ketones, by heating of alkoxyacetylenes and in the case of certain cyanoketenes by thermolysis of the cyclic precursors (162) and (163). 

In the preceding paragraphs we dealt with procedures where amino groups are introduced in the last step into halo- and alkoxyacetylenes which can eventually be prepared in situ by elimination from the corresponding haloalkanes and alkenes. 

The kinetic law is generally of the type rate = A 2 [acetylene] [H+]. In concentrated acid solutions, the plot of log koha vs H0 in the case of compounds 2 is linear with essentially unit slope (Noyce et al., 1965, 1967 Noyce and De Bruin, 1968). The study of the reaction in a series of buffers showed that it is subject to general acid catalysis (Noyce and Schiavelli, 1968a Stamhuis and Drenth, 1961) and the application of the Bunnett, Grunwald and similar treatments in the case of thio-alkoxyacetylene derivatives (Hogeveen and Drenth, 1963b) clearly indicate that the addition of a water molecule does not take place in the slow step of the reaction. 

Alkoxyacetylenes are obtained by alcohol and hydrogen halide elimination from dialkylacetals of a-chloroaldehydes, induced by NaNH, in liquid ammonia (equation 81)108. 4-Pentyn-l-ol is obtained in similar fashion (equation 82) . 

Before taking care of this hydride further, let us repeat the two processes Just described using structure XII as an imaginary starting material. This compound would be simply a tautomer of VIII. While the 1,5-hydrogen transfer (route C) should yield alkoxyacetylene XIII, the extrusion of nitrogen and hydride (route D) would afford compound XV, which features the same oxidation level as the target structure II. 

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. 

This cyclization reaction is not restricted to sulfone-stabilized carbanions. Indeed, phosphorus ylides, ester- and ketone-enolates participate also in the 5-endo-dig carbometallation reaction [17a]. The synthesis of fused bicyclo as well as spirobicyclo derivatives can be accomplished via the intramolecular carbometallation reactions of various stabilized carbanions with alkoxyacetylenes [17a]. Moreover, some asymmetric... 

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. 

Ketene aminals can be prepared from the reaction of orthoesters, alkoxyacetylenes or ketene acetals with excess secondary amine. 

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

Klein, M. Zabel, M. Bernhardt, G, Konig, B, Tetrahydroxy 10-membered cyclic enediynes. J. Org. Chem. 2003, 68. 9379-9383 Comanita, B.M. Heuft, M.A. Rietveld, T. Fallis, A.G. A mild route to a-alkoxyacetylenes mediated by Fewis acids and synthetic routes to 10-,ll- and 12-membered ring enediyne carbocycles. Israel J. Chem. 2000, 40, 241-253. 

Anisimov, K.N., and Kopylova, B.V., An investigation in the field of the derivatives of unsaturated phosphinic acids. Part 24. Reaction of phosphorus pentachloride with alkoxyacetylenes, Izv. Akad. Nauk SSSR, Ser. Khim., 277, 1961 Bull. Acad. Sci. USSR, Div. Chem. Sci. (Engl. Transl.), 253, 1961. 

An enantiosdective intermolecular Pauson-Khand reaction between nor-bomene and chiral alkoxyacetylene bearing 10-methylthioisobomeol as the auxiliary has recently been successfully performed with high selectivity [1676]. 

The first intramolecular carbolithiation of stabilized carbanions to the alkoxyacetylene... 

Alkoxyacetylenes add water at room temperature in presence of hydrochloric acid and mercury(n) acetate, yielding esters. 1-Phenoxy-l-hexyne (4.96 g) thus give phenyl hexanoate (2.8 g).95... 

Sodamide in liquid ammonia is a particularly suitable reagent for preparation of alkoxyacetylenes, e.g., methoxy-, ethoxy-, and butoxy-acetylene, from dialkyl chloroacetals 194 both hydrogen halide and the alcohol are split off in this process ... 

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