Alkenes Prins reaction

PdCb-CuCb catalyzes the condensation of branched-chain alkenes with formaldehyde to give the l,3-dioxanes 96a and 96b (Prins reaction)[73]. The yields are much higher than in the conventional acid-catalyzed Prins reaction. 

This type of polyhalo alkane adds to halogenated alkenes in the presence of AICI3 by an electrophilic mechanism. This is called the Prins reaction (not to be confused with the other Prins reaction, 16-53). ... 

The addition of an alkene to formaldehyde in the presence of an acid catalyst is called the Prins reaction.Three main products are possible which one predominates depends on the alkene and the conditions. When the product is the 1,3-diol or the dioxane, the reaction involves addition to the C=C as well as to the C=0. The mechanism is one of electrophilic attack on both double bonds. The acid first protonates the C=0, and the resulting carbocation attacks the C=C ... 

Ene and Carbonyl-Ene Reactions. Certain double bonds undergo electrophilic addition reactions with alkenes in which an allylic hydrogen is transferred to the reactant. This process is called the ene reaction and the electrophile is known as an enophile A When a carbonyl group serves as the enophile, the reaction is called a carbonyl-ene reaction and leads to [3,-y-unsalurated alcohols. The reaction is also called the Prins reaction. 

Cationic polymerization of alkenes and alkene derivatives has been carried out frequently in aqueous media.107 On the other hand, the reaction of simple olefins with aldehydes in the presence of an acid catalyst is referred to as the Prins reaction.108 The reaction can be carried out by using an aqueous solution of the aldehyde, often resulting in a mixture of carbon-carbon bond formation products.109 Recently, Li and co-workers reported a direct formation of tetrahydropyranol derivatives in water using a cerium-salt catalyzed cyclization in aqueous ionic liquids (Eq. 3.24).110... 

Reactions of the allylic position of alkenes with carbonyl or imine electrophiles are known as Prins reactions and have been discussed in previous sections (3.2.9). More examples of similar Alder-ene-type reactions (the Prins reaction) will be discussed in Chapter 8. 

During the coverage period of this chapter, reviews have appeared on the following topics reactions of electrophiles with polyfluorinated alkenes, the mechanisms of intramolecular hydroacylation and hydrosilylation, Prins reaction (reviewed and redefined), synthesis of esters of /3-amino acids by Michael addition of amines and metal amides to esters of a,/3-unsaturated carboxylic acids," the 1,4-addition of benzotriazole-stabilized carbanions to Michael acceptors, control of asymmetry in Michael additions via the use of nucleophiles bearing chiral centres, a-unsaturated systems with the chirality at the y-position, and the presence of chiral ligands or other chiral mediators, syntheses of carbo- and hetero-cyclic compounds via Michael addition of enolates and activated phenols, respectively, to o ,jS-unsaturated nitriles, and transition metal catalysis of the Michael addition of 1,3-dicarbonyl compounds. ... 

Alkylation with Carbonyl Compounds The Prins Reaction. Carbonyl compounds react with alkenes in the presence of Brpnsted acids to form a complex mixture of products known as the Prins reaction. The use of appropriate reaction conditions, solvents, and catalysts allows one to perform selective syntheses. Characteristically formaldehyde is the principal aldehyde used. Mineral acids (sulfuric acid, phosphoric acid), p-toluenesulfonic acid, and ion exchange resins are the most frequent catalysts. Certain Lewis acids (BF3, ZnCl2, SnCl4) are, however, also effective. 

Simple mono- and disubstituted alkenes react to yield 1,3-diols, when the Prins reaction is carried out at elevated temperature. Diols originate from the attack of water on carbocation 18, or through the acidolysis of dioxanes under the reaction conditions. When the reaction is conducted in acetic acid, monoacetates are formed by acetate attack on 18. Dienes resulting from the dehydration of intermediate diols are the products of the transformation of more substituted alkenes. Monoacetates and diols may react further to yield 1,3-diol diacetates. When the Prins reaction... 

Dioxacyclohexanes can be produced in excellent yields from aliphatic or aryl-substituted alkenes.64 Dilute sulfuric acid at or above room temperature with paraformaldehyde appears to give the best results. Dioxane-water or acetic acid as solvent was found to afford increased yields in the Prins reaction of arylalkenes. 

Few examples of the Prins reaction of homologous aldehydes and ketones are known.73,74 Acetaldehyde was shown to react smoothly with isobutylene under mild conditions, whereas other, less substituted alkenes were found to be very unreactive.73... 

The method ZC3Z + C is used for the preparation of reduced pyrimidines, oxazines and thiazines as well as for dioxanes, dithianes and oxathianes as mentioned above (e.g. 258 — 257, 259 Z, Z = NH, O, S). The Prins reaction yields 1,3-dioxanes (77S661) it involves the acid-catalyzed condensation of alkenes with aldehydes with 1,3-diols as intermediates. 

Heteropolyacids catalyze the Prins reaction of alkenes [Eq. (14)] more efficiently than H2SO4 and /j-toluenesulfonic acid (PTS). For example, H3PW12O40 is 10-50 times more active than H2S04 or PTS (162). In this reaction, oxocarbo-cations may be stabilized through complexation with heteropolyanions ... 

Prins reaction (cf 10, 186-187). Dimethylaluminum chloride is an effective catalyst for the ene addition of formaldehyde (as trioxane or paraformaldehyde) to mono- and 1,2-disubstituted alkenes.5 When 1.5-2.0 equiv. of the Lewis acid is used, homoallylic alcohols are obtained, usually in high yield. y-Chloro alcohols, formed by cis-addition of -Cl and -CH2OH to the double bond, are sometimes also observed when only 1 equiv. of the Lewis acid is present. The advantage of this reaction over the Prins reaction (using HC1) is that m-dioxanes are not formed as by-products, because formaldehyde no longer functions as a nucleophile when complexed to the Lewis acid. 

Prins reaction Conjugated dienes and activated alkenes react with aldehydes and carboxylic acids in the presence of ruthenium catalysts to give 1,3-diols. Variable amounts of acetoxybutene and higher molecular weight compounds can be formed. RuCl3 3H2Ocan be used, but the best results are obtained with 1. 

The Prins Reaction is the acid-catalyzed of addition aldehydes to alkenes, and gives different products depending on the reaction conditions. It can be thought of conceptually as the addition of the elements of the gem-diol carbonyl hydrate of the aldehyde across the double bond. 

The Prins reaction (electrophilic a-hydroxyalkylation of alkenes) is practicable with hydrogen fluoride as solvent and offers a possibility for the synthesis of fluorinated alcohols. 

Halofluoroalkanes participate in interesting additions to fluorinated alkenes in the presence of strong Lewis acids. Unfortunately, these modified Prins reactions are not entirely product-specific various minor isomers are formed. ... 

The reactions of alkenes with carbon electrophiles have already been mentioned in the cyclization of 1,5-dienes. However, carbon electrophiles may be generated in other ways. Protonation of formaldehyde (methanal) leads to a carbocation that may be stabilized by the oxygen lone pair (Scheme 3.12a). This may react with alkenes with the formation of 1,3-glycols or unsaturated alcohols, depending upon the way in which the intermediate carbocation is discharged (the Prins reaction, Scheme 3.12b). 

Coverage in this chapter is restricted to the use of alkenes or alkynes as enophiles (equation 1 X = Y = C) and to the use of ene components in which a hydrogen is transferred. Coverage in Sections 1.2 and 1.3 is restricted to ene components in which all three heavy atoms are carbon (equation 1 Z = C). Thermal intramolecular ene reactions of enols (equation 1 Z = O) with unactivated alkenes are presented in Section 1.4. Metallo-ene reactions are covered in the following chapter. Use of carbonyl compounds as enophiles, which can be considered as a subset of the Prins reaction, is covered in depth in Volume 2, Chtqiter 2.1. Addition of enophiles to vinylsilanes and allylsilanes is covered in Volume 2, Chapter 2.2, while addition of enophiles to enol ethers is covered in Volume 2, Chapters 2.3-2.S. Addition of imines and iminium compounds to alkenes is presented in Volume 2, Part 4. Use of alkenes, aldehydes and acetals as initiators for polyene cyclizations is covered in Volume 3, Chapter 1.9. Coverage of singlet oxygen, azo, nitroso, S=N, S=0, Se=N or Se=0 enophiles are excluded since these reactions do not result in the formation of a carbon-carbon bond. 

The acidic 10 and 12 membered ring zeolites (H-MOR, ZSM-5, ZSM-11) can also be used to catalyze the condensation of alkenes with aldehydes to form unsaturated alcohols, acetals etc. (Prins reaction)[92]. Chang et a/. [93] showed that this reaction involves in the initial step the activation of the aldehyde by a Bronsted acid site to generate an electrophilic species. The condensation with, e.g., isobutene leads then to a primary alcohol with a positive charge at the tertiary carbon atom. Elimination of water and addition of further aldehyde molecules may lead to a broad variety of products. Some of these reactions can be effectively blocked by chosing zeolites with the appropriate pore size [94,95]. 

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