Propargyl esters reactions

Propargylic (or 2-alkynyl) compounds are derivatives of alkynes. However, Pd-catalyzed reactions of propargylic derivatives, particularly esters and halides, are very different mechanistically from those of simple alkynes, except in a few cases. Therefore, the reactions of propargylic esters and halides are treated in this section separately from those of other alkynes. However, some reactions of propargylic alcohols, which behave similarly to simple alkynes, are treated in Section 6. 

Reaction between propargyl esters and organometallic reagents... 

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 Pd°-catalyzed transformation of enediynes represents a highly efficient and effective approach for the synthesis of polycyclic compounds, with different ring sizes being obtained by a variation of the tether [129]. In this respect, reaction of 6/1-270 led to the tricyclic product 6/1-271 as a single diastereomer. The initial step is a chemoselective hydropalladation of the propargylic ester moiety in 6/1-270 to give an alkenyl-Pd-species, according to the mechanism depicted in Scheme 6.71. A hexatriene is formed as a byproduct. 

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... 

An alternative, but related, route to allenic titanium reagents from propargylic esters has been reported recently. Reaction of titanocene dichloride with BuMgCl and Mg yields a reactive titanocene intermediate, formulated as Cp2Ti. This reduced Ti species reacts in situ by oxidative addition to propargylic acetates. The allenyltitanium reagents thus produced add to aldehydes and ketones, as expected, to afford homopropargylic alcohols (Table 9.27) [43]. 

The cationic iridium complex [Ir(cod)(PPh3)2]OTf, when activated by H2, catalyzes the aldol reaction of aldehydes 141 or acetal with silyl enol ethers 142 to afford 143 (Equation 10.37) [63]. The same Ir complex catalyzes the coupling of a, 5-enones with silyl enol ethers to give 1,5-dicarbonyl compounds [64]. Furthermore, the alkylation of propargylic esters 144 with silyl enol ethers 145 catalyzed by [Ir(cod)[P(OPh)3]2]OTf gives alkylated products 146 in high yields (Equation 10.38) [65]. An iridium-catalyzed enantioselective reductive aldol reaction has also been reported [66]. 

Oxybutynin Oxybutynin, 4-diethylamino-2-butynylic ester a-phenylclohexaneglycolic acid (14.1.35), is synthesized either by a Mannich reaction using propargyl ester of a-phenyl-a-cyclohexaneglycoUc acid, paraform and diethylamine, or transesterification of the methyl ester of a-phenyl-a-cyclohexaneglycolic acid using l-acetoxy-4-diethylamino-2-butene in the presence of sodium methoxide [26]. 

Fig. 12. Reaction of monoalkyl monohydrogen phthalate with aniline. [Ester] = [Amine] = 0.25 M, T = 70 °C, Solvent = DMSO-d6. ( ) trifluoroethyl ester ( ) 1,3-dichloroisopropyl ester ( ) ethylglycolyl ester (A) propargyl ester (T) methyl ester...

Chiral allenylboronic esters.1 The enantioselectivity in synthesis of homo-propargylic esters by the reaction of aldehydes with chiral allenylboronic esters (11, 181) is markedly increased by use of bis-2,4-dimethyl-3-pentyl esters of d- or vAaxtaric acid rather than the diethyl ester. Yields in the reaction of various saturated aldehydes are 70-90%, and optical yields are consistently greater than 90% and even higher (97-99%) when the aldehyde is present in excess. However, yields are poor in reactions with aryl and a,p-unsaturated aldehydes. This modified procedure was used in a synthesis of (S)-(—)-ipsenol (2) from d-(—)-bis(2,4-di-methyl-3-pentyl) tartrate (1) (equation I). 

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. 

The synthesis of dihydrofurans from propargyl esters is another reaction in which both gold and silver have been employed. In early work, Shigemasa et al.37 reported the efficient chirality transfer in the cycloisomerization of monoesters of butynediols. They used 8-15 mol% of AgBF4 as catalyst in benzene at 80°C in the dark. 

Polymer-supported synthesis of 1,3-dienes by efficient ruthenium-catalyzed in-termolecular enyne metathesis has been reported by Schiirer and Blechert [99]. The polystyrene resin, containing a propargyl ester moiety, was reacted with functionalized alkene in the presence of Cl2(PCy3)2Ru(=CHPh). The dienes obtained were cleaved from the polymer support using a paladium-catalyzed reaction with different nucleophiles (Eq. 57). 

Cycloaddition reactions of a,/3-unsaturated chromium and tungsten complexes have been studied to a great extent and have been reviewed.3 -6 Our report on cycloaddition of (l-alkynyl)carbene complexes is restricted to a short abstract and an update including more recent results. A most remarkable feature of [4+2] cycloadditions of 1,3 dienes to C=C bonds of (l-alkynyl)carbene complexes, e.g., li, is that such reactions proceed under very mild conditions, compared to those for reactions of propargylic esters, e.g., 41. Thus, formation of a Diels-Alder adduct, e.g., a norbornadiene derivative 42, can be achieved at 25°C via carbene complexes instead of at 190°C via the direct route (Scheme 15).68 Ligand disengagement from compound 40 can be achieved in various ways, e.g., by formation of an ester 43 through oxidation of the Cr=C bond, or by formation of an allyl silane 4369 or a stannane.70 71... 

Type III reaction proceeds by an attack of a nucleophile at the central sp carbon of the allenylpalladium. In contrast to facile Pd(0)-catalyzed reactions of allylic esters with soft carbon nucleophiles via TT-allylpalladium intermediates, propargylic esters are less reactive towards soft carbon nucleophiles. No reaction of soft carbon nucleophiles occurs with propargylic acetates. However, soft carbon nucleophiles such as -keto esters and malonates react with propargylic carbonates under neutral conditions using dppe as a ligand [43]. 

Hydrostannation can also be catalyzed by palladium compounds. Other tin hydrides may react by a polar rather than a radical mechanism. A series of PVC stabilisers (the Estertins) have been developed by the AKZO company, and which are prepared by the reaction of HCl with metallic tin or SnCla, to give the solvated chlorotin hydrides H2SnCl2 and HSnCls, respectively, which add, in a heterolytic Michael fashion to acrylic or propargylic esters [e.g. Equations (1.7) and (1.8)] the chlorides are then converted by anion exchange into the thioglycollates. 

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