Aryl homoallyl ethers

Palladium-catalyzed oxidative cyclization of aryl homoallyl ethers affords 4-methyl-2//-chromenes in moderate yield. The reaction is proposed to proceed via activation of the alkene by coordination to Pd(ll) followed by intramolecular nucleophilic attack by the arene. Subsequent [1-hydride elimination and isomerization then affords 4-methyl-27/-chromenes (Scheme 13). Electron-rich aryl homoallyl ethers give the best yield and good regio-selectivity is observed for the reaction of unsymmetrical arenes <2005OL3355>. 

Gold(lII) chloride and silver hexafluoroantimonate can also be used as catalyst for addition reactions of electron-rich arenes and heteroarenes to olefins. In a similar fashion, the intramolecular hydroarylation of aryl homoallyl ethers and related substrates takes place upon heating with AuCb and AgOTf in dichloroethane to 80 °C and affords dihydrobenzopyrans, tetrahydroquinolines, and tetralins with good yield (Scheme 4-18). ... 

DMSO, H2O, 90°, 79-87% yield. These conditions are only effective for primary allylic and homoallylic, primary benzylic, and aryl TBDMS ethers. ... 

Aryl homoallyl ketones and 4-methoxy phenyl ethers are also good substrates for the AD [8], whereas the structurally related allyl amides and thioesters give products with insufficient enantioselectivity. Homoallylic 4-methoxy benzoates perform relatively poor, which is consistent with Corey s proposed mechanistic model [9],... 

Maiti and Roy reported a selective method for deprotection of primary allylic, benzylic, homoallylic and aryl TBS ethers using aqueous DMSO at 90° C. All other TBS-protected groups, benzyl ethers, THP ethers as well as methyl ethers remain unaffected. 

In the presence of 1 cquiv. or less of trimethylsilyl triflate these crotylsilancs react with aryl acetals to form homoallylic ethers with high diastereo- and enantiosclectivity. The new C-C bond (CsQ) is formed with high syn-selectivity (13-40 1). 

Two approaches for the synthesis of allyl(alkyl)- and allyl(aryl)tin halides are thermolysis of halo(alkyl)tin ethers derived from tertiary homoallylic alcohols, and transmetalation of other allylstannanes. For example, dibutyl(-2-propenyl)tin chloride has been prepared by healing dibutyl(di-2-propenyl)stannane with dibutyltin dichloride42, and by thermolysis of mixtures of 2,3-dimethyl-5-hexen-3-ol or 2-methyl-4-penten-2-ol and tetrabutyl-l,3-dichlorodistannox-ane39. Alternatively dibutyltin dichloride and (dibutyl)(dimethoxy)tin were mixed to provide (dibutyl)(methoxy)tin chloride which was heated with 2,2,3-trimethyl-5-hexen-3-ol40. 

Enantioselective ally lotion.1 The reaction of 2 with allylmagnesium chloride in ether affords a chiral orange allyltitanium complex 3. This complex reacts with an aldehyde at —78° to afford homoallyl alcohols in 55-88% yield and in 86-94% ee and with release of 1 and a titanate that can be reconverted to CpTiCl3 (equation I). Reaction of 3 with aryl ketones requires a temperature of 0°, and the enantioselectiv-ity is only about 50%. 

Carbanions derived from a-sulfonyl ethers 5 undergo [2.3] sigmatropic rearrangement the resulting a-hydroxy sulfoties are subject to a further fragmentation, yielding an aryl sulfinic acid and an aldehyde which reacts further with excess alkyllithium Lo afford a secondary homoallylic alcohol61 66. 

In numerous synthetic studies it has been demonstrated that DMP can be used for a selective oxidation of alcohols containing sensitive functional groups, such as unsaturated alcohols [297,1215-1218], carbohydrates and polyhydroxy derivatives [1216, 1219-1221], silyl ethers [1222,1223], amines and amides [1224-1227], various nucleoside derivatives [1228-1231], selenides [1232], tellurides [1233], phosphine oxides [1234], homoallylic and homopropargylic alcohols [1235], fluoroalcohols [1236-1239] and boronate esters [1240]. Several representative examples of these oxidations are shown below in Schemes 3.349-3.354. Specifically, the functionalized allylic alcohols 870, the Baylis-Hillman adducts of aryl aldehydes and alkyl acrylates, are efficiently oxidized with DMP to the corresponding a-methylene-p-keto esters 871 (Scheme 3.349) [1217]. The attempted Swern oxidation of the same adducts 870 resulted in substitution of the allylic hydroxyl group by chloride. 

Under conditions of high dilution to prevent intermolecular reactions, two allylic halide groups in the same molecule can be coupled to give a cyclic product. Macrocyclic lactones have been made in this way. Coupling occurs only at the primary centres. Note that the nickel reagents do not attack ester groups. Neither do they react with acid chlorides, ethers, nitriles, olefins or alkyl, aryl or vinyl chlorides (in contrast to bromides or iodides). Aldehydes and cyclic ketones are attacked, however, above 40°C affording homoallylic alcohols. 

A further application of Ca-chiral aryl selenides derived from D-mannitol has appeared this year [see Vol 28, p.375]. Reagent 389 (from 388) promotes enantioselective selenoetherifications and selenolactonizations. Homoallylic alcohols 390 and 391 are converted to cyclic ethers 392 and 393 with >98% and 94% d.e., while p,y-unsaturated acids 394 and 395 formed lactones 396 and 397 in >98% and 92% d.e., respectively. 

Using a combination of AuClg/AgOTf as the catalytic system, Jean and Weghe realized a gold-catalyzed intramolecular hydroarylation of unactivated olefins, which provided a facile access to dihydrobenzopyrans, tetralins, and tetrahydro-quinolines 122 (Scheme 12.53) [57]. A variety of homoallyl aryl ethers 121 with... 

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