By the Prins reaction

Terpenoid Synthesis from Isoprene.—Interest continues in new syntheses of iso-prene and its derivatives the dioxan (37) is obtained108 in good yield by the Prins reaction of methylallyl chloride with formaldehyde (cf. Vol. 5, p. 8) free-radical addition of isopropyl alcohol to vinyl acetate yields compound (38) which gives isoprene by acid-catalysed reaction over alumina.109 (Z)-2-Methylbut-2-en-l-ol and dimethylallyl alcohol are readily available from frans-crotyl alcohol.110... 

Bi(III) is an efficient catalyst for the formation of tetrahydropyran-4-ols from homoallylic alcohols by the Prins reaction application to styrenes leads to 1,3-dioxanes <05SC1177> cr i-2,6-Disubstituted tetrahydropyrans are selectively formed in a Bi-mediated intramolecular oxa-conjugate addition of a,P-unsaturated ketones 10 the actual catalyst is considered to be the Bronsted acid derived from the Bi salt <05TL5625>. cat. BiXa... 

Structurally related to rose oxide is the hydroxypyran shown in Scheme 4.17. This material is known under the tradenames Florosa and Florol . It is prepared by the Prins reaction between isoprenol and isovaleraldehyde. 

The formation of tetrahydropyrans by the Prins reaction The oxo-ene mechanism Stereoselectivity in the Prins reaction... 

Addition of formaldehyde dimer to alkenes with in the gas phase by the Prins reaction are studied at the MP2(fc)/6-31G(d,p). It is shown that the initially complex obtained at the first study turn into 1,3-dioxane without intermediate formation of a a-complex. Also shown, that transformation of 7i-cation is a pseudo synchronous process. 

Vakulin, I. V. (2002). Research of heterocycle formation by the Prins reaction and their... 

FIGURE 10.3 Potential energy surface of 1,3-dioxane formation by the Prins reaction. 

The role of formaldehyde dimer in 0-containing heterocycles formation by the Prins reaction have been investigated. It was shown that the 1,3-di-oxanes, hydrogenated pyrans and oxetanes can be can be obtained from formaldehyde dimers and alkenes in the gas phase. The activation energy of these reactions is different. It is lower for 1,3-dioxanes formation, and higher for oxetanes formation. Thus formation of 1,3-dioxanes happens in the conditions of kinetic control. Opposite, the hydrogenated pyrans formation happens in the conditions of thermodynamic control... 

Uses ndReactions. The Prins reaction of 3-carene with formaldehyde in acetic acid gives mainly 2-carene-4-methanol acetate, which when saponified produces the 2-carene-4-methanol, both of which are commercial products of modest usage (60). 3-Carene (28) also reacts with acetic anhydride with a catalyst (ZnCl2) to give 4-acetyl-2-carene (29) (61), which is also a commercial product. Although 3-carene does not polymerize to produce terpene resins, copolymerization with phenol has been successfully commercialized by DRT in France (62). 

Formaldehyde also reacts with butadiene via the Prins reaction to produce pentenediols or their derivatives. This reaction is cataly2ed by a copper-containing catalyst in a carboxyUc acid solution (57) or RuCl (58). The addition of hydrogen also proceeds via 1,2- and 1,4-addition. 

The Prins reaction often yields stereospecifically the and-addition product this observation is not rationalized by the above mechanism. Investigations of the sulfuric acid-catalyzed reaction of cyclohexene 8 with formaldehyde in acetic acid as solvent suggest that the carbenium ion species 7 is stabilized by a neighboring-group effect as shown in 9. The further reaction then proceeds from the face opposite to the coordinating OH-group " ... 

The formation of complex mixtures of products by a Prins reaction can be a problem. An example is the reaction of aqueous formaldehyde with cyclohexene 8 under acid catalysis ... 

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). ... 

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... 

C) with an indole-like odor. It is prepared by a Prins reaction from indene and formaldehyde in the presence of dilute sulfuric acid [194]. It is used in perfumes for soap and detergents. 

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... 

The stereochemistry of the Prins reaction is complex. In the transformation of cyclohexene and 2-butenes anti stereoselective addition was observed,67-69 whereas syn addition of two formaldehyde units takes place in the formation of 1,3-dioxanes from substituted styrenes.70 Most of the transformations are, however, nonstereo-selective,71 72 accounted for by carbocation 18. 

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. 

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). 

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 is attacked by the C=C to give 85. 

---