Halogenated acetals

Other Reactions of Phospholipids. The unsaturated fatty acid groups in soybean lecithin can be halogenated. Acetic anhydride combined with the amino group of phosphatidylethanolamine forms acetylated compounds. PhosphoHpids form addition compounds with salts of heavy metals. Phosphatidylethanolamine and phosphatidjhnositol have affinities for calcium and magnesium ions that are related to interaction with their polar groups. 

These reaction conditions were applicable to the thiol esters of alkanoic, heteroaromatic, and halogenated acetic acids. 

Ketene acetal synthesis by /1-elimination of haloacids from halogenated acetals under well controlled conditions using thermal activation (A), ultrasound (US) or micro-wave irradiation [92] (MW) has been described. From a mechanistic point of view, as the TS is more charge delocalized than the GS and the polarity is enhanced during the course of the reaction, a favorable microwave effect can therefore be observed (Eqs. (37) and (38) and Scheme 3.13). 

The diazonium compound itself is liberated by adding a strong organic acid, such as halogenated acetic acid, after the coupling component has been introduced into the reaction mixture. 

The first step in the submonomer method involves the acylation of a halogenated acetic acid on the resin under standard conditions. In the second step the side chain of the peptoid is introduced by nucleophilic substitution of the halide with an excess of the primary amine. 

Keywords a-halogen acetal, a-haogen thioacetal, KOtBu, microwave irradiation, /(-elimination, ketene O,O-acetal, ketene 5,5-acetal... 

A cold mixture (0°C) of the halogenated acetal (2 mmol), 5% of tetrabutylam-monium bromide (TBAB) (0.1 mmol), if it is necessary, and the appropriate base were introduced into a Pyrex tube which was then placed in a Synthewave 402 Prolabo microwave reactor fitted with a rotational system. Microwave irradiation was carried out for the time and at the power indicated. The crude reaction was purified by distillation or extraction to obtain the product. 

Woolard FX, Moore RE, Roller PP (1979) Halogenated Acetic and Acrylic Acids from the Red Alga Asparagopsis taxiformis. Phytochemistry 18 617... 

When benzotellurophene dioxinate was refluxed in benzene with equimolar amounts of halogenated acetic acids, one oxinate group was exchanged for an acetate group3. 

The carbinol precursor of propoxyphene is made by treating the Mannich base 21a with a benzyl Grignard reagent. The major (a) diastereoisomer 21b is separated, resolved with (+)-camphor-10-sulfonic acid, and finally acylated to yield the active drug. Pyrrolidino analogs of propoxyphene are more potent than the parent (acetate, 2 x, propionate,1 x pethidine in mice),(51) while the halogenated acetates 22 (X = F or Cl) have similar activities to morphine in mice.(58) Replacement of terminal phenyl of propoxyphene by 2-pyridyl achieves a potency rise, as occurs also in the cyclic analog 23/59 ... 

The preceding data are consistent with hydride transfer being predominantly an interfacial reaction in sulfuric acid. This view is supported by studies of the effect of acid modifiers on the reaction in 96% H2SO4. Table I shows the effect of halogenated acetic acids, methanesulfonlc acid and water upon the hydride transfer rate. The rates were estimated in two ways and all rates are relative to that in 96 percent H2SO. ... 

The relative rates were estimated both from dp/dt slopes and from the total gas evolved after 1 minute. The data Indicate that as the acid Is weakened by H2O addition, the hydride transfer reaction slows down. On the other hand, the addition of many of the halogenated acetic acids and methanesulfonlc acid results, at least Initially, In a slight rate Increase. 

Malonic acid, ethyl malonate, and their monoalkyl derivatives can be readily halogenated in ether solution subsequent decarboxylation leads to the corresponding a-halogenated acetic acid in 55-80% yield. The reaction of the potassium salts of monoethyl alkylmalonates with bromine provides the a-bromo esters directly, although the yields ate relatively low. ... 

Many functional groups, such as halogen, acetal, ketone, and acetate, and in some cases alcohol, aldehyde, and amide, can survive during the Kolbe decarboxylation [44], Double bonds isolated from the carboxylic acid moiety are usually not affected under the... 

Alkynylation of oxiranes or oxetanes with lithium alkynides is effectively carried out in the presence of BF3 OEt2 at -78 C. The use of BF3 gives better results than TiCU, SnCU or AlCU. The reaction takes place stereospecifically with anti opening, and the attack generally occurs at the less hindered site. Several functional groups such as halogens, acetals or certain esters survive the reaction conditions (Scheme 16). 100-102... 

Figure 1.3 Boil ing points of halogenated acetic acids as a function of molecular weight. Circles are fluorinated acetic acids.

Sampling of halogenated acetic adds was carried out using glass tubes coated with alkaline glycerol (Frank et al. 1995). 

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