Esters, allenic functionalized, synthesis

The addition of secondary amines to acetylenes is most applicable to the synthesis of conjugated acyclic enamines (50,171,172). Particularly the addition to acetylenic esters and sulfones has been investigated (173-177) and it appears that an initial trans addition is followed by isomerization to more stable products where the amine and functional group are in a trans orientation (178). Enamines have also been obtained by addition of secondary amines to allenes (179). 

There is not just one predominating method for the generation of alienes with at least one electron-withdrawing group, but a number of important routes. Even for the synthesis of alienes with a given acceptor function, for example allenic esters, different routes are often used such as the Wittig reaction, prototropic isomerization or alkoxycarbonylation. 

Scheme 23 /S-Allenic sulfoxides in the one-pot synthesis of functionalized 4-oxo-2-alkenoate esters...

Zhao, G., Shi, Y. and Shi, M. (2005) Synthesis of functionalized 2ff-l-benzopyrans by DBU-catalysed reactions of salicylic aldehydes with allenic ketones and esters. Organic Letters, 7, 4527 530. 

Two different types of tandem reactions for the synthesis of highly functionalized cyclohexenones cyclopropyl-substituted propargyl esters initiated rhodium-catalysed Saucy-Marbet 1,3-acyloxy migration have been reported (Scheme 152). The resulting cyclopropyl-substituted allenes derived from acyloxy migration followed by 5 -f 1-cycloaddition with carbon monoxide. ... 

Methanesulfonates. The most common use of methanesulfonyl chloride is for the synthesis of sulfonate esters from alcohols. This can be readily accomplished by treatment of an alcohol with mesyl chloride in the presence of a base (usually Triethy-lamine or Pyridine). The methanesulfonates formed are functional equivalents of halides. As such they are frequently employed as intermediates for reactions such as displacements, eliminations, reductions, and rearrangements. Selective mesylation of a vicinal diol is a common method of preparation of epoxides." Alkynyl mesylates can be used for the synthesis of trimethylsilyl allenes. Oxime mesylates undergo a Beckmann rearrangement upon treatment with a Lewis acid. Aromatic mesylates have been used as substrates for nucleophilic aromatic substitution. Mesylates are more reactive than tosylates toward nucleophilic substitution, but less reactive toward solvolysis. 

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