2-methoxy-1-propene, reaction with

Jacobsen and co-workers14 have shown that a tridentate Schiff base chromium complex 13 catalyzed an asymmetric carbonyl-ene reaction between a variety of aryl aldehydes (14, Equation (8)) and 2-methoxy propene 15 or 2-trimethylsiloxypropene. The highest yields were afforded when the aryl ring was substituted with an electron-withdrawing group however, the substituent did not seem to affect the enantioselectivity. 

The second example concerns the study of acetonation of o-mannose (see Scheme 8) and allows a clear distinction between the use of 2,2-dimethoxypropane and 2-methoxy-propene. Thus, whereas D-matmose gives 2,3 5,6-di-0-isopropylidene-D-mannofuranose 5 by reaction of the free sugar with acetone [5,6] as well as with 2,2-dimethoxypropane [96], the major compound (more than 85%) obtained with 2-methoxypropene is 4,6-0-isopropylidene-D-mannopyranose 6 [52]. Once again, a confirmation of the better stability of furanoid acetals in this series is given by the selective hydrolysis of the 2,3 4,6-di-O-isopropylidene-D-mannopyranose 7 (by-product of the preceding reaction or quantitatively obtained by action of 2-methoxypropene on acetal 6), witch gives the furanoid monoacetal 8. Actually, the pyranoid monoacetal 9 can be easily prepared as soon as the anomeric hydroxyl group is protected by acetylation [52]. 

Silyl-l,3-dienes undergo anodic methoxylation in methanol to give 1,4-addition products with an allylsilane structure as intermediates. Therefore, they are further oxidized to give l,l,4-trimethoxy-2-butene derivatives as the final products. The products are easily hydrolyzed to provide the corresponding y-methoxy-a, /t-unsaUirated aldehydes. Since 1-trimethylsilyl-l,3-dienes are readily prepared by the reaction of the anion of l,3-bis(trimethylsilyl)propene with aldehydes or ketones, l,3-bis(trhnethylsilyl)propene offers a, /i-formylvinyl anion equivalent for the reaction with carbonyl compounds (equation 15)16. 

On the contrary, the reaction of l-phenylthio-l-trimethylsilyl-2-propene 5257 with alkyllithium afforded the Z-l-phenylthio-l-trimethylsilyl alkenes 51 and the reaction of 1-methoxy-l-phenylthio-l-trialkylsilylalkanes 5458 provided a highly stereoselective synthesis of Z-l-phenylthio-l-trialkylsilylalkenes 53 (Scheme 35). 

In recalcitrant cases, e.g., in the formation of trans-fused dioxolanes, 2-methoxy-propene (isopropenyl methyl ether, bp 34 °C) or 2-(trimethylsilyloxy)propene (bp 93 °C)3S can be used [Scheme 3.24J.36 The latter reaction benefits from the formation of hexamethyldisiloxane [(Me Si O] to drive the reaction to comple-tion. One of the prime advantages of using 2-methoxypropene for the formation of isopropylidene derivatives is that the conditions are very mild the reaction is fast even with weak add catalysts such as pyridinium p-toluenesulfonate [Scheme 3.25].37... 

A mixture of 324 g (3 mols) of anisole and 4 g of concentrated H3P04 was heated to 150° C. in a 500 mL. capacity reaction vessel equipped with a thermometer, stirrer and dropping funnel. After the above-mentioned temperature had been reached, 64 g (0.432 mol) of o-anethole (2-methoxy-propen-l-yl benzene) were introduced into the thoroughly stirred anisole/phosphoric acid mixture over a period of 1 hour, followed by stirring for 1 hour at the same temperature. The excess anisole was then distilled off at 50° C./5 Torr, leaving 110 g of a condensation product consisting predominantly of the o,p -isomers of 1,1-dimethoxy diphenyl propane. The yield was substantially quantitative. 

Dihydrofuran derivatives 319 are formed as major products in Rh2(OAc)4-catalyzed reactions of a-diazoacetophenone with 2-methoxy-propene or a-methoxystyrene (84MI1). Copper chelate or rhodium(II) acetate-catalyzed 1,3-dipolar cycloaddition of metal carbenoids, generated from ethyl formyldiazoacetate (90JOC4975), ethyl diazopyruvate... 

Ti(IV). Carreira has reported a novel class of tridentate ligands whose complexes with Ti(IV) 48 serve as catalysts for a variety of enantioselective aldehyde additions [20J. The reactions that have been examined include acetate and dienolate aldol additions as well as ene-like reactions of 2-methoxy propene [21], The salient features of these catalytic systems include the fact that a wide range of aldehyde substrates may be utilized, the ability to carry out the reaction employing 0.2-5 mol% catalyst loading, and the experimental ease with which the process is executed. The typical experimental procedure prescribes the use of an in situ generated catalyst, at -10 to 23 °C in a variety of solvents, employing as little as 0.5 mol% catalyst. 

A side-chain methylsulphonylimino group attached to C-3 of a pyran-2-one ring acts as a l-azadiene in an inverse electron Dtels-Alder reaction with l,I-di-methoxy-l-propene at ambient temperature. The first-formed product is more conveniently isolated after removal of the A -SOiMe and MeO functions with t-butoxide at -30°C. 

An alternative approach to the synthesis of acitretin has been reported from enone 25 (Scheme 9),(42,43) Reduction of 25 followed by addition of acetylene afforded alcohol 29 in 67% yield. Treatment of 29 with 2-methoxy-l-propene in the presence of p-TsOH, followed by reaction with NaOH afforded diene 30. Treatment of 30 with wo-butyl chloroacetate yielded triene 32 via epoxide intermediate 31. Treatment of 32 with PBra and A, iV-dimethylacetamide followed by ester saponification completed a synthesis of acitretin in 6 steps and 25% overall yield. 

The Lilanium(lV) chloride mediated reactions of the silylketene acetal, l-methoxy-2-methyI-l-trimethylsilyloxy-l-propene. with a-methylthioaldehydes afford predominantly adducts resulting from chelation control, besides minor amounts of the diastereomers10. 

The reaction of phenyl-1,2-propadiene with iodine bromide in MeOH afforded a 100% yield of 2-iodo-3-phenyl-3-methoxy-l-propene whereas the reaction in CS2 at 0°C provided a l 4mixture of 2-iodo-3-phenyl-3-bromo-l-propene and l-phenyl-2-iodo-3-bromo-l-propene [16]. The corresponding chlorination shows a lower regios-... 

Another cycloaddition to an a,(3-unsaturated compound involves the reaction of nitrile oxides with 3-methoxy- or 3-methylthio-1 -phenyl-2-propene-1 -one (Scheme 6.18) (133,134). The isoxazoles that are isolated are considered to arise from the respective intermediate isoxazolines by subsequent elimination of methanol or methanethiol. The regioselectivity observed was attributed to the presence of substituents with strong electron-donating ability, and this was accommodated in terms of the FMO theory (133,134). 

A mixture of 50 g l-(3-methoxy-4,5-methylenedioxyphenyl)-2-nitro-propene and 26 g racemic a-methylbenzylamine was heated on the steam bath. The mixture gradually formed a clear solution with the steady evolution of nitroethane. When the reaction became quiet, there was added a mixture of 20 mL concentrated HC1 in 100 mL H20. The reaction mixture dissolved completely, and as the temperature continued to rise there was the abrupt solidification as the formed myristicinaldehyde crystallized out. This product was removed by filtration and, when combined with a second crop obtained by the hexane extraction of the filtrate, gave 36.9 g of myristicinaldehyde. The mp of 128-129 °C was raised to 133-134 °C by recrystallization from hexane. 

Formaldehyde reacts with isoeugenol [l-(3-methoxy-4-hydroxyphenyl)propene] in alkaline medium to give a 1,3-dioxane derivative via an unusual Prins-type reaction.192... 

Intermolecular addition of carbon nucleophiles to the ri2-pyrrolium complexes has shown limited success because of the decreased reactivity of the iminium moiety coupled with the acidity (pKa 18-20) of the ammine ligands on the osmium, the latter of which prohibits the use of robust nucleophiles. Addition of cyanide ion to the l-methyl-2//-pyr-rolium complex 32 occurs to give the 2-cyano-substituted 3-pyrroline complex 75 as one diastereomer (Figure 15). In contrast, the 1-methyl-3//-pyrrolium species 28, which possesses an acidic C-3-proton in an anti orientation, results in a significant (-30%) amount of deprotonation in addition to the 2-pyrroline complex 78 under the same reaction conditions. Uncharacteristically, 78 is isolated as a 3 2 ratio of isomers, presumably via epimerization at C-2.17 Other potential nucleophiles such as the conjugate base of malononitrile, potassium acetoacetate, and the silyl ketene acetal 2-methoxy-l-methyl-2-(trimethylsiloxy)-l-propene either do not react or result in deprotonation under ambient conditions. 

This reaction of silyl ketene acetals with aldehydes, using 29 as a stoichiometric chiral reagent (Eq. 46), was reported by Reetz et al. [42]. The aldol addition of l-(trimethyl-siloxy)-l-methoxy-2-methyl-l-propene and 3-methylbutanal provides the aldol in only 57 % yield, but with 90 % ee. 

Kinetics of isomerization of glyceraldehyde to dihydroxyacetone—and the formation of pyruvaldehyde from both— have been studied in sub- and super-critical water. Formaldehyde reacts with isoeugenol [l-(3-methoxy-4-hydroxyphenyl)propene] in alkaline medium to give a 1,3-dioxane derivative via an unusual Prins-type reaction. The potential-energy surface for the equihbriimi, HCO - - HCN H2CO - - CN, has been calculated by ab initio methods. 

Alkylation of amidine 1131 with l-bromo-2-methoxy-2-propene affords regiospecifically N-alkylated product 1132. Treatment of 1132 with pyridinium />-toluenesulfonate in aqueous THF provides imidazole 1133 in good yield. In this reaction, l-bromo-2-methoxy-2-propene is used as a protected form of a-bromoacetone, which itself leads to poor yields when reacted directly with amidines (Scheme 275) <2000J1V1E3168>. 

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