Ethers, allyl propargyl

Shortly after Trost s works, two investigations demonstrated the high reactivity of platinum halide salts for this type of reactions. Blum reported a PtCU-catalyzed rearrangement of allyl propargyl ethers to 3-oxabicyclo[4.1.0]-heptenes (Scheme 79).294 This series of reactions also represented the premiere entry into the versatile formation of cyclopropyl products based on skeletal rearrangements of enynes.295 This intriguing aspect is discussed further. 

This ring contraction has been used to provide the ten-membered ring of the germacranolide aristolactone (4) from a 13-membered allylic propargylic ether. 

Dehydrobromination of 219 with DBU gave rise to allyl propargyl ethers 220, which underwent a base-catalyzed isomerization-[4 +2]-cycloaddition sequence to afford tricyclic enol ethers 221 [179]. 

N. Moufid and Y. Chapleur, Radical cyclization of allyl propargyl ethers and acetals application to the stereocontrolled acylation of carbohydrates, Tetrahedron Lett. 32 1799 (1991). 

The Rh-catalysed silylcarbocyclization of the allyl propargyl ether (589) with silane gives 592. The reaction starts by the insertion of the triple bond to the Rh-SiR3 bond... 

Cyclization of allyl propargyl ethers.2 This Pd complex is far superior in re-... 

Sigmatropic Wittig rearrangement of macrocyclic allyl propargyl ethers to carbocycles 91TA1. 

Cycloisomerization of allyl propargyl ethers takes place under mild conditions when performed with a ruthenium hydride catalyst obtained from Cp RuCl(COD) in the presence of acetic acid or ethanol. 3,4-Dialkylidenete-trahydrofurans were produced in good yields [ 71 ] (Eq. 53). It is noteworthy that the C-H and C-C bonds formed are always syn. This is the result of the cis addition of the Ru-H bond to the C=C bond. 

Allyl propargyl ethers are easily cyclized to tetrahydrofuran derivatives by titanocene- and zirconocene-mediated reactions. Thus, these compounds are convenient starting materials for the stereoselective synthesis of highly substituted 3-alkylidenetetrahydrofurans (Scheme 72) <1996TL9059>. It is noteworthy that the titanocene- and zirconocene-mediated reactions show opposite (Z)/( )-selectivities. 

Platinum(ll)-catalyzed carbocyclization of a.ty-enynes has been intensively researched lately. For instance, 2-disubstituted l-en-6-ynes react with methanol in the presence of PtCl2 as catalyst to form carbocycles with exocyclic aUcenes. The analogous reactions of 3-allyl propargyl ether or 3-allyl propargyl tosylamine in water using the same catalysts will generate cyclopropyl aldehydes besides the product of cycloisomerization (Scheme 82). The coordination of the... 

A formal synthesis of the natural product aucubigenone by Billington has made use of a very direct route involving Pauson-Khand cycloaddition of an allyl propargyl ether (Scheme 21). ... 

We prefer Pauson-Khand reactions for the other two compounds as they have both been mace that way. The first needs a simple allyl propargyl ether readily formed from the adduct of aceuier. i and acetone and allyl bromide. The cobalt carbonyl complex gives a good yield of ere cyclopentenone. 

Table 5 2,3-Wittig Rearrangement of Allyl Propargyl Ethers...

Nonracemic (Z)-allylic propargyl ethers likewise rearrange with excellent enantioselectivity (Table 7). In these examples the configuration of the starred center in (114) and (115) should be opposite for ( )-and (Z)-products owing to the concerted suprafacial nature of the rearrangement. The stereochemistry at the carbinyl center is related to the equatorial/axial preference of the alkynyl grouping (Scheme 7). It should be noted that the ( )-products (114) and (115) are greatly favored because of repulsive 5yn-l,3 in-... 

Table 7a 2,3-Wittig Rearrangement of Nonracemic Allylic Propargylic Ethers Derived fiom (5)-Lactaldehyde. OSiBu Me2...

Allyl propargyl ethers are also good substrates for the Wittig rearrangement. Deprotonation of the propargyl position is relatively facile. 

The catalytic [2 + 2 + 1]-cycloaddition reaction of two carbon—carbon multiple bonds with carbon monoxide has become a general synthetic method for five-membered cyclic carbonyl compounds. In particular, the Pauson-Khand reaction has been widely investigated and established as a powerful tool to synthesize cyclopentenone derivatives.110 Various kinds of transition metals, such as cobalt, titanium, ruthenium, rhodium, and iridium, are used as a catalyst for the Pauson-Khand reaction. The intramolecular Pauson-Khand reaction of the allyl propargyl ether and amine 91 produces the bicyclic ketones 93, which bear a heterocyclic ring as shown in Scheme 31. The reaction proceeds through formation of the bicyclic metallacyclopentene intermediate 92, which subsequently undergoes insertion of CO to give 93. 

In order to introduce substituents to a macro-cyclic framework in a stereoselective fashion, a 12,31 Wittig rearrangement of the corresponding macroeyclie allyl propargyl ether is an attractive strategy. Bulyllilhium in hexane-THI- promoted... 

Claisen rearrangement. Allyl allenyl ethers resulting from isomerization of allyl propargyl ethers with t-BuOK are ready to undergo Claisen rearrangement. A route to a-substituted acroleins is established. 

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