Enol ethers 2-methoxypropene

This catalyst is also active toward the simple enol ether 2-methoxypropene.1... 

The authors successfully applied their protocol to the alternative enol ether 2-methoxypropene (MOP) to prepare the MOP ether 1-8 from a subset of the various alcohol substrates as depicted in Scheme 6.21. This high-yielding (92-97%) MOP protection occurred smoothly at room temperature MOP turned out to be so reactive that the uncatalyzed reaction also proceeded albeit at lower rates [118, 145]. 

Pentafluoro-3-methoxypropene (1) has been found to isomcrizc spontaneously over a period of several days at room temperature to the fluorinated enol ether 2.5(1... 

The oldest known method for producing isopropylidene acetals is treatment of a diol with anhydrous acetone under acid catalysis. However, in order to trap the resulting water it is also necessary to include molecular sieves or copper sulfute 2-Methoxypropene (19) is roughly twice as expensive as acetal 18. but as an enol ether it is also more reactive. In especially problematic cases one can in addition resort to 2-trimethylsilyIoxypropene (IPOTMS = isopropenyl-oxytrimethylsilane) (20), but lor this situation it is inappropriate on the basis of cost. 

In many instances the reaction of an alcohol with dihydropyran (or ethyl vinyl ether or 2-methoxypropene) does not go to completion despite the addition of a large excess of the enol ether as much as 20% of the starting material will be present at equilibrium. The equilibrium, once reached, can be shifted toward product by adding excess finely powdered anhydrous potassium carbonate and stirring the reaction mixture at room temperature. As the acid concentration gradually diminishes, the reaction goes to completion. 

On heating methylbutenol (9.21) with 2-methoxypropene (9.27) (which is the methyl enol ether of acetone), a /ra .v-etherification occurs with the elimination of methanol and the formation of the allyl vinyl ether (9.28). This ether is perfectly set up for a Claisen rearrangement, which it undergoes, to produce methylheptenone (9.5). 

Carriera and coworkers employed titanium SchifFbase catalysts such as (7.189) (see Section 7.1) in an ene reaction of 2-methoxypropene (7.190) with various aldehydes (7.01) (not especially reactive ones). The overall synthetic strategy of using 2-methoxypropene (7.190) has significant merit in comparison with aldol reactions, because it is a cheap starting material, and means that a silyl enol ether does not have to be prepared prior to an aldol reaction. The Schiff base chromium complexes such as (7.192) developed by Jacobsen and coworkers is effective with both aliphatic and aromatic aldehydes providing up to 96% ee in the reaction of the latter type of substrate with 2-methoxypropene (7.190). This complex also catalyses the ene reaction with 2-silyloxypropene with high ee. ... 

But the Merck chemists noticed that amino alcohol itself, certainly once protected, has a remarkable similarity to Evans oxazolidinone auxiliaries anyway, and it turns out that this amino alcohol will function very successfully as a chiral auxiliary, which does not need to be removed, avoiding waste and saving steps The amino alcohol was acylated with the acyl chloride, and the amide was protected as the nitrogen analogue of an acetonide by treating with 2-methoxypropene (the methyl enol ether of acetone) and an acid catalyst. The enolate... 

The development of the new tridentate ligand-titanium complex 67, by Carreira et al. allows the use of silylketene acetals as substrates. 3-Hydroig esters were obtained in high yields and enantioselectivities (Scheme 7.40). In addition, cheap and easily available 2-methoxypropene was found to be a suitable alternative to silyl enol ethers. 

Structure (332) in which either R or R is H and one of the three dotted lines represents a double bond. As discussed above and shown in Fig. 8.10, dehydrolinalool (46) can be treated with an acetone equivalent, such as 2-methoxypropene, to yield il -ionone directly without going through citral, if the desired product is an ionone as opposed to a methylionone (402). Diketene (403) and acetoacetate esters (403) have also been used. Similarly, the methyl enol ether of 2-butanone can react with dehydrolinalool to give o-methyl-i >-ionone (404). 

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