Alkoxyacetylenes esters

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. 

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

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... 

The reaction of alkoxide ions with alkynyliodonium salts is unproductive, leading to only decomposition products rather than the desired alkoxyacetylenes. Similarly, reaction of R3SiO does not lead to any siloxyalkynes. In contrast the softer sulfonate, carboxylate, and phosphate nucleophiles all readily react with alkynyliodonium salts leading to the corresponding alkynyl sulfonate, carboxylate and phosphate esters [4]. 

Silyl ynol ethers have highly characteristic spectral properties. The triple bond stretching in the IR of siloxyalkynes is at 2260-2270 cm" which compares with that of ynol esters and alkoxyacetylenes (see Sections III and IV of the present review) ". Particularly noteworthy and characteristic are the acetylenic carbon signals in the NMR. The... 

Alkoxyalkynes have characteristic spectral properties . The triple bond stretching in the IR of alkoxyacetylenes varies from 2290 cm in 1-ethoxyhexyne to 2130-2160 cm in the parent" " and silylated" alkoxyethynes. The signals of both acetylenic carbons in the NMR are located in the normal alkyne region of 80-90 ppm f , which is distinctly different from siloxyacetylenes (see Section II.D.l) and ynol esters (Section IV.B). The mass spectra of alkoxyacetylenes almost always have a peak for the molecular ion and easily identifiable, characteristic fragmentation" " . ... 

Analogously to siloxy- and alkoxyacetylenes (see Sections II.D.2 and III.C.4), alkynyl esters are good partners in [2+2] cycloaddition reactions. A typical example of such a reaction is the cycloaddition of benzoate 116 and tosylate 128 with azete 126 (equations 78... 

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