Reaction with propargyl acetates

PhMe2Si)2CuLi reacts with allylic acetates via stereospecific (anti) conjugate displacement of the acetate group to afford allylsilanes in excellent yields7 Similar stereospecificity is observed in reactions with propargyl acetates. ... 

No reaction of soft carbon nucleophiles takes place with propargylic acet-ates[37], but soft carbon nucleophiles, such as / -keto esters and malonates, react with propargylic carbonates under neutral conditions using dppe as a ligand. The carbon nucleophile attacks the central carbon of the cr-allenylpal-ladium complex 81 to form the rr-allylpalladium complex 82, which reacts further with the carbon nucleophile to give the alkene 83. Thus two molecules of the a-monosubstituted /3-keto ester 84, which has one active proton, are... 

Dienes can be obtained from silylallenes by protodesilylation using boron trifluo-ride-acetic acid complex (equation 29)62. Since silylallenes can be obtained by the reaction of propargyl acetate with cuprous reagent derived from chloromethyltrimethylsilane, this reaction sequence constitutes conversion of propargylic acetate to butadiene through one carbon homologation. 

The first examples of allene syntheses using copper-mediated SN2 substitution processes are documented for the reaction of propargylic acetates 7 with lithium dialkyl-cuprates, which led to the formation of allenes 8 with moderate to good chemical yields (Scheme 2.2) [2]. 

In the area of allenic non-natural product chemistry, the synthesis of the [34]alle-nophane 14 (Scheme 2.4) is particularly noteworthy, with all four of its allenic bridges being formed through subsequent SN2 substitution reactions of propargylic acetates with a methyl magnesium cuprate [14] (see Section 2.5 for an alternative synthesis of macrocyclic allenes). 

The reaction of propargylic acetates with excess lithium dialkyl-cuprates [Eq. (98)] in ether between —10° and — 5°C affords a novel... 

Allylsilanes. The Se2 reaction of the cuprate (2) derived from 1 with tertiary allylic acetates results in stereospecific onri-reaction to provide allylsilanes. Similar stereospecificity is observed in reaction of 2 with propargyl acetates to form alicnylsilanes. Examples ... 

Analogous to the allylation with allylsilanes and -stannanes, the transformations, vinylallylation, propargylation, allenylation, alkenylation, alkynylation, and arylation, are viable by the use of an appropriate reagent in the presence of a titanium Lewis acid these are surveyed in the review articles cited both in the Introduction and in this section. The stereochemistry of the reaction of a (vinylallyl)silane in the presence of TiCU has been reported [234]. Equation (113) shows that the major reaction of this silane and isobutyraldehyde occurred mainly in the anti sense with a ratio of anti to syn attack of 90 10 at the terminus remote from the silyl group. Essentially the same stereochemical outcome was observed for the same reaction with the corresponding trimethylsilyl derivative. The intramolecular reaction with an acetal, however, proceeded less selectively the anti syn ratio was 60 40 (Eq. 114) [234]. 

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]. 

Aldiough the Nicholas reaction is a reliable method for propargylation of silyl enolates, it requires a stoichiometric amount of alkyne-Co2(CO)6 complexes [260]. Recently, Matsuda et al. successfully used the Ir-catalyzed system for highly regioselective propargylation of silyl enolates with propargyl acetates (Scheme 10.97) [261]. 

Oxazolidines are obtained in good to excellent yields by the palladium(II)-catalyzed cyclization of A-Boc protected iV-allyl-A -hydroxymethylamines (191) <94CC357>. The palladium species is regenerated by molecular oxygen in DMSO (Scheme 94). Allyl carbamoylmethyl ethers cyclize to oxazolidines by reaction with mercuric acetate <89H(28)663>. Silver triflate catalyzes the cyclization of (9-propargyl isoureas to 4-alkylidene-oxazolidines with high diastereoselectivity <88CC1175>. 

Base lb also catalyzes the deacetylation of protected alcohols under mild conditions in quantitative yields [138]. The reaction with propargyl alcohol is very selective because the reactive acetylene functionality is not affected. In contrast, DIBAL-H is known to react with acetylenes. Secondary and tertiary alcohol acetates also were deacetylated in excellent yields and it is interesting that the latter alcohols do so without undergoing side reactions such as elimination. 

Allylic geminal dicarboxylates 285 are prepared by Pd-catalyzed reaction of propargyl acetate 284 with AcOH [104], Two products 287 and 288 are obtained from gem-allylic compounds 286, and 288 is an allylic ester and undergoes the second allylation. Several applications to asymmetric syntheses have been reported [48]. Reaction of 289 with dimethyl methylmalonate afforded 290 with 95% ee. 

The Pd-catalyzed reaction of PhZnCl with propargyl acetates and related electrophiles has produced Ph-substituted allenes, which proceeded with inversion at the propargyl carbon atom [195, 196] (Eq. (1), Scheme 3.50). This reaction provides a useful and selective route to stereodefined allenes. On the other hand, recent developments of Ni-catalyzed reactions of ArZn with propargyl halides that produced propargyl products, are noteworthy [197, 198] (Eq. (2), Scheme 3.50). 

Treatment of 4-pentynoic acids with propargyl acetates in the presence of palladium diacetate, tri(2-furyl)phosphine and potassium carbonate in DMSO affords 5- E)- 2-allenylidene)-tetrahydro-2-furanones (Scheme 30). Employment of potassium carboxy-lates generated by the reaction of 4-pentynoic acids with KOBu-t produces lower yields. 

Other rearrangements in this class include the allylacetylene-vinylallene isomerization with various substituent groups the reaction of methyl-magnesium iodide and magnesium iodide with propargyl acetates the... 

The reaction of propargylic acetates with 2-oxocyclohex-3-enecarboxylates in the presence of a palladium catalyst affords 7-methylenebicyclo[3.2.1]oct-3-en-2-ones in a highly diastereoselective manner (Scheme 6.43) [48]. 

Scheme 3-167. Reaction of silyl enol ethers with propargyl acetates.

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