Reaction with isopropenyl formate

With aldehydes, primary alcohols readily form acetals, RCH(OR )2. Acetone also forms acetals (often called ketals), (CH2)2C(OR)2, in an exothermic reaction, but the equiUbrium concentration is small at ambient temperature. However, the methyl acetal of acetone, 2,2-dimethoxypropane [77-76-9] was once made commercially by reaction with methanol at low temperature for use as a gasoline additive (5). Isopropenyl methyl ether [116-11-OJ, useful as a hydroxyl blocking agent in urethane and epoxy polymer chemistry (6), is obtained in good yield by thermal pyrolysis of 2,2-dimethoxypropane. With other primary, secondary, and tertiary alcohols, the equiUbrium is progressively less favorable to the formation of ketals, in that order. However, acetals of acetone with other primary and secondary alcohols, and of other ketones, can be made from 2,2-dimethoxypropane by transacetalation procedures (7,8). Because they hydroly2e extensively, ketals of primary and especially secondary alcohols are effective water scavengers. 

As in 0-52 hydrazides and hydroxamic acids can be prepared from carboxylic esters, with hydrazine and hydroxylamine, respectively. Both hydrazine and hydroxylamine react more rapidly than ammonia or primary amines (the alpha effect, p. 351). Imidates RC(=NH)OR give amidines RC(=NH)NH2. Lactones, when treated with ammonia or primary amines, give lactams. Lactams are also produced from y- and 8-amino esters in an internal example of this reaction. Isopropenyl formate is a useful compound for the formylation of primary and secondary amines,897... 

Isobutyl chloroformate is most frequently applied in peptide chemistryfollowed by ethyl chloto-formate (see Table 1). The advantage of this method is that the mixed anhydride does not have to be isolated, and during work-up only carbonic acid half esters are formed, which decompose to an alcohol and carbon dioxide. Only in the case of sterically hindered amino acids does the opening of the anhydride at the undesired carbonyl occur in considerable amounts. Furthermore, short activation times (30 s) at low temperatures lead to peptides with minimal racemization. With isopropenyl chloroformate the mixed anhydride is prepared at room temperature, and during reaction only acetone and carbon dioxide are formed. 

The allylic alcohol 209 obtained from 3-(m-methoxyphenyl) propanol and isopropenyl magnesium bromide in THE at - 78 C was converted to the ketone 210 by a chloroketal Claisen reaction. ° Reaction with isopropenyllithium followed by reduction of the resulting allylic epoxide (211) resulted in formation of the tetramethyl allylic alcohol 212. Cyclization with stannous chloride" afforded an 85 15 mixture of 213 214 ozonolysis of 213 afforded 215, the route... 

Nilsson " has reported the reaction of isopropenyl acetate with MA. Products including 166, 167, and 168 were obtained. A mechanism for their formation was proposed as follows ... 

Formation of alkyne dimers with a GO inserted was observed in the thermal reactions of Fe3(GO)i2 with isopropenyl-acetylene two isomeric open clusters 3a and 3b were isolated and characterized by X-ray diffraction. In contrast, the thermal reactions of internal propargylic alcohols with Fe3(GO)i2 led to pentanuclear acetylide derivatives, obtained upon elimination of aldehydes or chetones from the alkynes (Figure 1). ... 

Isopropenyl Acetate as a Source of Acetone. Under certain reaction conditions, isopropenyl acetate reacts to deliver an equivalent of acetone for acetonide formation or for oxidative addition to an enol. Under acidic conditions, isopropenyl acetate has been used to generate isopropylidene derivatives of malonic acids. Isopropenyl acetate also undergoes an oxidative addition reaction with ketones in the presence of Manganese(IlI) Acetate An acetone subunit is added to the a-position of a ketone to give a 1,4-diketone. 

Reaction conditions depend on the reactants and usually involve acid or base catalysis. Examples of X include sulfate, acid sulfate, alkane- or arenesulfonate, chloride, bromide, hydroxyl, alkoxide, perchlorate, etc. RX can also be an alkyl orthoformate or alkyl carboxylate. The reaction of cycHc alkylating agents, eg, epoxides and a2iridines, with sodium or potassium salts of alkyl hydroperoxides also promotes formation of dialkyl peroxides (44,66). Olefinic alkylating agents include acycHc and cycHc olefinic hydrocarbons, vinyl and isopropenyl ethers, enamines, A[-vinylamides, vinyl sulfonates, divinyl sulfone, and a, P-unsaturated compounds, eg, methyl acrylate, mesityl oxide, acrylamide, and acrylonitrile (44,66). 

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... 

However, the equilibrium monomer concentrations of disubstituted alkenes is measurable. The equilibrium constants for dimerization, tri-merization, and polymerization of a-methylstyrene have been determined as a function of temperature under anionic conditions [12] similar values should be obtained under cationic conditions. Unfortunately, the equilibrium position can t be determined directly under cationic conditions due to the irreversible side reactions of isomerization and indan and spirobiindan formation (Section II. A). The equilibrium monomer concentrations of isobutene and isopropenyl vinyl ethers should also be relatively high, albeit lower than those of a-methylstyrenes. However, the true equilibrium can t be reached with these monomers due to irreversible side reactions, and reliable data are therefore not available. Nevertheless, the ceiling temperature of isobutene polymerization is apparently between 50 and 150° C. 

Deprotonation of la-lc with methyllithium in ether at -78 °C leads to spontaneous elimination of lithimntrimethylsiloxide according to a modified Peterson mechanism and formation of the unstable silenes 2a-2c. In absence of trapping agents these undergo dimerization reactions, 2a leading to l-isopropenyl-2-isopropyl-l,l,2,2-tetrakis(trimethylsilyl)disilane (3) (Scheme 1). 

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