Propargylic esters rearrangement

The ester/alkyne rearrangement system can be extended by conjugation to involve a more distant site. The reaction of diethyl phosphorochloridate with 3-methylhex-4-yne-2-ene-l-ol leads to the vinylogous propargylic ester rearrangement as shown in Equation 4.39.176... 

Further mechanistic work with optically active and labeled compounds confirmed that the rate-determining step in such rearrangement was the silver coordination to the alkyne moiety and revealed that the silver-catalyzed allene epimerization was 2-40 times faster than the propargyl ester rearrangement.53... 

Rearrangement of acetylenic sulphenates to the allenic sulphoxides 151 was discovered when the synthesis of propargylic ester of trichloromethanesulphenic acid 152 was attempted (equation 86). This reaction is of general scope and gives very good yields of allenic sulphoxides (Table 14) from structurally diverse cohols and various sulphenyl chlorides Reaction of alkynols 153 with benzenesulphenyl chloride in the presence... 

The first syntheses of a-allenic a-amino acids [131,133] took advantage of Steg-lich s [134] protocol for the oxazole-Claisen rearrangement of unsaturated N-ben-zoylamino acid esters (Scheme 18.46). Thus, treatment of the propargylic ester 143 with triphenylphosphine and tetrachlormethane furnished the allenic oxazolone 144, which was converted into the amino acid derivative 145 by methanolysis. Stepwise deprotection finally led to the allenic DOPA analog 146, which shows a much higher decarboxylase-inhibiting activity than a-vinyl- and a-ethynyl-DOPA [133],... 

Further variations of the Claisen rearrangement protocol were also utilized for the synthesis of allenic amino acid derivatives. Whereas the Ireland-Claisen rearrangement led to unsatisfactory results [133b], a number of variously substituted a-allenic a-amino acids were prepared by Kazmaier [135] by chelate-controlled Claisen rearrangement of ester enolates (Scheme 18.47). For example, deprotonation of the propargylic ester 147 with 2 equiv. of lithium diisopropylamide and transmetallation with zinc chloride furnished the chelate complex 148, which underwent a highly syn-stereoselective rearrangement to the amino acid derivative 149. 

In a similar way, propargyl esters of A -benzoyl-a-amino acids have been converted into a-allenyl-a-amino acid esters 113 by cyclization to oxazoles 111 followed by Claisen rearrangement to the 4-allenyl-2-phenyl-5(4//)-oxazolones 112. Oxazolone ring opening with methanol then afforded 113 (Scheme 7.32). ... 

The ester enolate Claisen rearrangements of amino acid propargylic esters (106) have been used137 to produce a-allenic amino acids (107), and y, d-un saturated amino acids... 

Rearrangements of propargyl esters with silver salts were first mentioned by Zakharova in the mid-1940s.49 He described the conversion of 3-chloro-3-methyl-but-l-yne into a mixture of acetates in which the allenic acetate, l-acetoxy-3-methylbut-1,2-diene, was the major compound (Scheme 3.30). Although this product could arise from a silver assisted SN2 reaction, it could also be produced from the substitution product through rearrangement, probably catalyzed by silver ions. 

Similarly, 1-halo-l-sulfonylallenes (139) have been prepared by heating in toluene at 80 °C of propargyl esters (138) via [2,3]sigmatropic rearrangement of the latter (Scheme 32) [51]. 1-Bromo-l-sulfonylallenes 139, when treated with bromine, undergo attack on central allenic carbon with formation of intermediate carbenium bromide followed by hydrogen bromide eUmination, and afford stereospecifically the 2,3-dibromo-l-sulfonyl-l,3-dienes 140. 

The isomerization of propargylic alcohols to a, -unsaturated carbonyl compounds can also be effected by means of the rearrangement of derived propargylic esters (5) via allenic esters (6 equation 13). ... 

Pudovik. A.N.. and Aladzheva, I.M., Thermal or pseudo-Claisen rearrangement of allyl and propargyl esters of phosphorous acid, Dokl. Akad. Nauk SSSR, 151, 1110, 1963 Dokl. Chem. (Engl. Transl.), 151, 634, 1963. 

While rearrangement of propargylic esters to allenyl esters is facile, denouement of such intermediates is highly dependent on the presence of other multiple CC bonds in juxtaposi-tion. In any event, the generation of polycyclic compounds in one synthetic operation deserves serious consideration of the method for exploitation in the construction of significant and complex target molecules. 

Rearrangement. 2-Pivaloxy-l,3-dienes are formed by treatment of the corresponding propargylic esters with the Au(I) complex. ... 

Rearrangement. Rearrangement of propargylic esters as promoted by (Ph3P)AuNTf2 affords a-iodinated enones in the presence of NIS and a solvent system of acetone and water (800 l)at0°. ... 

The same catalyst was used by Li and co-workers for an efficient annulation of electron-rich phenols or naphthols with cyelic dienesJ Tricyclic or tetracyclic benzofuran derivatives were obtained as mixtures of syn and anti isomers with the former predominating. The reaetion probably proceeds by intermolecular C-C bond formation via addition of the phenol to the activated diene, followed by protodeauration and intramolecular formation of the C-O bond. In a related transformation, naphthalenes were obtained by treatment of aryl-substituted propargyl esters with eationic gold(I) eatalysts. The reaction may proceed via consecutive 1,3- and 1,2-rearrangements to afford conjugated dienes that then undergo an intramolecular hydroarylation. 

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