Ethoxy allylation

Ethoxy-allyl)-phenyl- -ethylester XII/1, 259f. (a-Ethoxycarbonyl-benzyl)-phenyl- -methylester E2, 220... 

Cyclohexen ( + )-l-Acetoxy-2,6-dimethyl-6-ethoxycarbonyl-E15/1, 76 (Keton + R-COOH) Cyclopentan 2-(3-Ethoxy-allyl)-2-ethoxycarbonyl-l-oxo- E15/1. 295 (Claisen-Umlager.) Cyclopropan 2,3-Diethoxycarbonyl-l-(2-methyl-l-propenyl)- E17a, 237 (subst. Cyclopropen + ROOC en-COOR) E18, 891 (Cyclopropen 4- En) 5,8-Dioxa-spiro 3.4 oct-l-en 2-Butyl-(or tert.-ButyI)-1 -isopropyloxy-3-oxo- E17f, 805 [l,2-(OR)j —4 OSiRj — 4-R — 3-oxo —cyclobuten + l,2-(OSiR3)2 — ethan] Ethan 1,1-Diethoxy-2-(4-methoxy-phenoxy)- E6b/1, 94 f, [OH -> 0-CH2-CH(0R)2]... 

The diastereoselectivity of BFa-promoted additions to benzaldehyde by cis-y-ethoxy allylic stannanes has been found to vary considerably with the nature of the a substituent [51]. Unbranched alkyl groups favor the syn adduct whereas branched alkyl substitution leads to mainly anti adducts (Table 34). Similarly, CH2TMS and CH2TBS substituents both afford a predominance of the anti adducts. 

Table 34. Diastereoselectivity of BF3-promoted additions of (E)-y-ethoxy allylic stannanes to benzaldehyde as a function of the a-substituent.

The ( )-vinylsilane 151 was prepared by treatment of the silylstannation product 150 with hydrogen iodide[75] and the silylzincation product with water[70]. The silylstannylation of 1-ethoxyacetylene proceeds at room temperature using Pd(OAc)i and 1,1,3,3-tetramethylbutyl isocyanide regioselec-tively and an Si group is introduced at the ethoxy-bearing carbon. Subsequent Cul- and Pd-catalyzed displacement of the stannyl group in the product 152 with allyl halide, followed by hvdrolvsis, affords the acylsilane 153[79],... 

NBS, CH3CN, H2O, 62-90% yield.The POM group has been selectively removed in the presence of an ethoxy ethyl ether, TBDMS ether, benzyl ether, p-methoxybenzyl ether, an acetate, and an allyl ether. Because the hydrolysis of a pentenyl 2-acetoxyglycoside was so much slower than a pentenyl 2-benzyloxyglycoside, the 2-benzyl derivative could be cleaved selectively in the presence of the 2-acetoxy derivative. The POM group is stable to 75% AcOH, but is cleaved by 5% HCl. 

The cleavage proceeds by initial reduction of the nitro groups followed by acid-catalyzed cleavage. The DNB group can be cleaved in the presence of allyl, benzyl, tetrahydropyranyl, methoxy ethoxy methyl, methoxymethyl, silyl, trityl, and ketal protective groups. 

The synthesis of the right-wing sector, compound 4, commences with the prochiral diol 26 (see Scheme 4). The latter substance is known and can be conveniently prepared in two steps from diethyl malonate via C-allylation, followed by reduction of the two ethoxy-carbonyl functions. Exposure of 26 to benzaldehyde and a catalytic amount of camphorsulfonic acid (CSA) under dehydrating conditions accomplishes the simultaneous protection of both hydroxyl groups in the form of a benzylidene acetal (see intermediate 32, Scheme 4). Interestingly, when benzylidene acetal 32 is treated with lithium aluminum hydride and aluminum trichloride (1 4) in ether at 25 °C, a Lewis acid induced reduction takes place to give... 

Allylic bromination, with A -bromosuccinimide (NBS), of 4-ethoxy-l,2-dihydrocyclo-pent[rf]azepine (8), formed by ethylation (with Meerwein s reagent) of the corresponding 4-oxo derivative, followed by in situ dehydrobromination of the resulting bromo compound with basic alumina, produces a low yield of l-bromo-2-ethoxycyclopent[c/]azepine (9) as a photosensitive, sapphire-blue, crystalline solid.55... 

Ethoxy-l,3,2-oxazaphospholidine 59 was prepared as a single diastereomer from (-)ephedrine (42) and ethyl dichlorophosphite 57. Its Arbusov reaction with allyl bromide gave the corresponding allyl phosphonates 61a,b as a diastereomeric mixture which could be separated by flash column chromatography and crystallization (Scheme 21) [48], On applying a similar protocol, starting from... 

A-trityl-(l/ ,2S)-norephedrine (58), the corresponding allyl phosphonates 62a,b were obtained via the Arbusov rearrangement of 2-ethoxy-1,3,2-oxazaphospholidine 60. The absolute configuration of the major diastereomer, 62a was determined by X-ray as (2S1,45,51 ).The reaction of the major diastereomer of allyl phosphonates 61a and 62a with DBU afforded the corresponding vinylphosphonates 63a,b (Scheme 21) [48], Nucleophilic addition to these resulted in induction of chirality at the [1-position of the stereogenic phosphorus atom in the initially produced diastereomeric phosphonates 64 or 65 (Scheme 21) [48],... 

Palladium-catalyzed cross-coupling of 19 with allyl bromide occurs exclusively at the vinylstannane moiety to give 1-ethoxy-1-silyl-1,4-diene 20. The following ether exchange with allyl alcohol causes the Glaisen rearrangement to give an acylsilane derivative 21 (Scheme 64).2... 

The allyl cation thus formed may stabilize itself either by readdition of the leaving group — leading to a 2,3-dihalopropene — or by the addition of a nucleophile. The influences of steric and electronic effects on the stereochemistry and on the solvolysis rates of various alkyl-substituted chlorocyclopropanes have been investigated by Parham and co-workers [165, 166], who could show for example that os-2,3-dipropyl-l,l-dichlorocyclopropane solvolyzes 24 times faster than its trans-isomer, in accordance with predictions based on orbital symmetry arguments. When one propyl substituent of the trans-isomer is replaced by an ethoxy group the rate of solvolysis increases 200 fold. 

To a solution of 9.7 g 2-allyl-4,5-dimethoxyphenol in a few mL EtOH, there was added a solution of 2.8 g KOH in 25 mL boiling EtOH followed by 5.5 g ethyl bromide. The mixture was held at reflux for 3.5 h and then poured into 200 mL H20 and extracted with 3x100 mL CH2C12. Pooling the extracts and removal of the solvent under vacuum gave a residue of 10.4 g of 4,5-dimethoxy-2-ethoxy-l-allylbenzene as a clear, mobile oil. It was substantially a single component by GC and was used in the following isomerization step without further purification. 

Deprotection of allyl aryl ethers is accomplished by protonolysis with palladium on activated charcoal in methanol solution in the presence of toluene-p-sulphonic acid,42 or by reduction with sodium bis(2-methoxy-ethoxy)aluminium hydride in toluene solution43 (Aldrich). This latter reagent also cleaves aryl benzyl ethers. 

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