Allene carboxylic ester

Among interesting olefin syntheses with ester phosphonates are those with the allenic aldehydes (141) and with the steroidal epoxy-aldehyde (142). The yield of allenic carboxylic esters has been increased to... 

Similarly, but using Se instead of Te, R-(+)- and 5 -(-)-jV,jV-dimethyl-l-ferrocenylethylamine provide [R,S-(Fc Se)2l (m 98-100" from hexane) and [S,R-(Fc Se)2] (m 103" from hexane) respectively as red solids, and these catalysts induce highly enantioselective selenoxide elimination to produce axially chiral allene carboxylic esters with high enantiomeric excess [Nishibayashi et al. Tetrahedron lett 35 3115 1994],... 

It has been shown that chirality does not necessarily need to be located on a tetrahedral carbon atom, as in the case of the fran -epoxy dicarboxylates (Scheme 2.33) [238]. For example, the axial chirality of the racemic iron-tricarbonyl complex [239] and of the allenic carboxylic ester shown below [240], was well recognized by PLE. 

A number of references cover similar syntheses of allenes with carboxylic acids [131, 139-142] and amides [143] instead of carboxylic esters as electron-withdrawing... 

Enzymes such as pig liver esterase have been successfully applied in enantioselective hydrolysis of allenyl esters on a scale of 2 mmoles131. This provides the enantiomerically enriched allene-carboxylic acid as well as the ester of opposite configuration, by what is in fact a catalytic kinetic resolution (6-90% oy). Conversely, partial enantioselective esterification of /1-hydroxy-allenes (3-72% oy) employing lipases has been reported132,133. 

Allene carboxylic acids have been cyclized to butenolides with copper(II) chloride. Allene esters were converted to butenolides by treatment with acetic acid and LiBr. Cyclic carbonates can be prepared from allene alcohols using carbon dioxide and a palladium catalyst, and the reaction was accompanied by ary-lation when iodobenzene was added. Diene carboxylic acids have been cyclized using acetic acid and a palladium catalyst to form lactones that have an allylic acetate elsewhere in the molecule. With ketenes, carboxylic acids give anhydrides and acetic anhydride is prepared industrially in this manner [CH2=C=0 + MeC02H (MeC=0)20]. 

The results of the following experiments give important clues for mechanistic considerations. Isolation of a trienecarboxylate ester as a hypothetical intermediate is not possible in most cases. As an exception, the trienecarboxylate 127 was isolated (64%) as a mixture with the cyclized product 128 (22%) after 4h reaction of 126. Compound 127 was converted to the cyclized product 128 on further exposure to the carbonylation conditions, showing that the allenecarboxylate 127 is a precursor of the cyclized product 128 (Scheme 11-36). Also, the carbonylation of the 1,4-enyne 129 gave only the allene carboxylate 130 (Scheme 11-37). No further carbonylation to give the cyclic ketone 131 or 132 was observed. In addition, the 1,3-diene ester 133 was recovered intact under the same carbonylation conditions without giving the cyclized product 134 (Scheme 11-38). 

Allen and coworkers identified esters through the formation of N-substituted tetra-chlorophthalimides by reacting them with potassium tetrachloriophthalimide in DMF or DM SO. Most of their examples were carboxylate esters, but 2-chloroethyl p-toluene-sulphonate was also tested by them291. 

A number of cycloaddition reactions involving allene derivatives as dienophiles have been recorded. Allene itself reacts only with electron-deficient dienes but allene carboxylic acid or esters, in which a double bond is activated by conjugation with the carboxylic group, react readily with cyclopentadiene to give 1 1 adducts in excellent yield. For example, the allene 12 gave, with very high yield and selectivity, the cycloadduct 13, used in a synthesis of (-)-P-santalene (3.19). An allene equivalent is vinyl triphenylphosphonium bromide, which is reported to react with a number of dienes to form cyclic phosphonium salts. These can be converted into methylene compounds by the usual Wittig reaction procedure (3.20). 

Instead of allenic carboxylic acids, the corresponding esters can also be used as substrates for gold-catalyzed cyclization reactions. Thus, heating t-butyl allenoates with gold(III) chloride in dichloromethane afforded butenolides in high yield (Scheme 4-104). In a similar way, Backvall et obtained 5-lactones by... 

BFg-etherate added at 0° to a soln. of trimethylsilylketene and tert-butanol in chloroform, and the product isolated after 5 min. product. Y 93%. - Trimethylsilylketene is a powerful acylating agent. F. e., also prepn. of a-allene-carboxylic acid esters (cf. Synth. Meth. 28, 851), s. R. A. Ruden, J. Org. Chem, 39,3607 (1974). 

Ethyl chrysanthemate (ethyl 2,2-dimethyl-3 c and t -[2-methylpropenyl]-cyclopropane carboxylate) [97-41-6] M 196.3, b 98-102 /llmm, 117-121 /20mm. Purified by vacuum distn. The free trans-acid has m 54° (from, EtOAc) and the free cis-acid has m 113-116° (from EtOAc). The 4-nitrophenyl ester has m 44-45° (from pet ether) [Campbell and Harper J Chem Soc 283 1945 IR Allen et al. JOrg Chem 21 29 1957]. 

Since 3-methylenecyclobutane-l,2-dicarboxylic anhydride is easily converted to 3-methyl-2-cydobutene-l,2-dicarboxylic acid, it is an intermediate to a variety of cyclobutenes. The dimethyl ester of 3-methylenecyclobutane-l,2-dicarboxylic acid is also a versatile compound on pyrolysis it gives the substituted allene, methyl butadienoate, and on treatment with amines it gives a cyclobutene, dimethyl 3-methyl-2-cyclobutene-l,2-di-carboxylate. ... 

Silyl esters have also been transformed successfully [137] another example reports the O-acylation of serine with a /l-alkynyl carboxylic acid anhydride accompanied by an in situ isomerization of the alkyne to the allene [138],... 

The acidity of the propargylic proton of the starting compound 18 allows the equilibration with the allene 19 induced by bases such as tertiary amines or alcoholates (Scheme 7.4). Such prototropic rearrangements furnish the title compounds 19 with at least one proton at the terminal carbon atom, often in good yields. The EWG group involves carboxylic acids [33], esters [34], ketones [35, 36], isonitriles [37], sul-fones [38], sulfoxides [39, 40] and phosphonates [41], The oxidation of easily accessi-... 

The photolysis of the furan derivatives 78 yielded the butadienals 79 as the main products [123], Further isomerizations leading to allenic esters used the radiation of a cyclopropene-1 -carboxylic acid ester [124] or applied flash vacuum pyrolysis to 3 -ethoxy cyclobut- 2-en-l-one[125]. 

The nucleophilic addition of alcohols [130, 204-207], phenols [130], carboxylates [208], ammonia [130, 209], primary and secondary amines [41, 130, 205, 210, 211] and thiols [211-213] was used very early to convert several acceptor-substituted allenes 155 to products of type 158 and 159 (Scheme 7.25, Nu = OR, OAr, 02CR, NH2, NHR, NRR and SR). While the addition of alcohols, phenols and thiols is generally carried out in the presence of an auxiliary base, the reaction of allenyl ketones to give vinyl ethers of type 159 (Nu = OMe) is successful also by irradiation in pure methanol [214], Using widely varying reaction conditions, the addition of hydrogen halides (Nu= Cl, Br, I) to the allenes 155 leads to reaction products of type 158 [130, 215-220], Therefore, this transformation was also classified as a nucleophilic addition. Finally, the nucleophiles hydride (such as lithium aluminum hydride-aluminum trichloride) [211] and azide [221] could also be added to allenic esters to yield products of type 159. 

Access to the corresponding enantiopure hydroxy esters 133 and 134 of smaller fragments 2 with R =Me employed a highly stereoselective (ds>95%) Evans aldol reaction of allenic aldehydes 113 and rac-114 with boron enolate 124 followed by silylation to arrive at the y-trimethylsilyloxy allene substrates 125 and 126, respectively, for the crucial oxymercuration/methoxycarbonylation process (Scheme 19). Again, this operation provided the desired tetrahydrofurans 127 and 128 with excellent diastereoselectivity (dr=95 5). Chemoselective hydrolytic cleavage of the chiral auxiliary, chemoselective carboxylic acid reduction, and subsequent diastereoselective chelation-controlled enoate reduction (133 dr of crude product=80 20, 134 dr of crude product=84 16) eventually provided the pure stereoisomers 133 and 134 after preparative HPLC. 

Efforts have been made to find stereoselective routes which provide disubstituted azetidines. Palladium catalysed cyclization of an enantiomer of allene-substituted amines and amino acids gives the azetidine ester 2 and a tetrahydropyridine in variable yield and ratio, depending on the substituents and conditions <990L717>. The (TRIS)- and (253I )-isomeis of the substituted azetidine-2-carboxylic acids 3 (R = COjH) are obtained in several steps from the corresponding 3 (R = CHjOSiMejBu ) which, in turn, is produced in high yield by photochemical intramolecular cyclization <98HCA1803>. 

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