Formaldehyde Prins reaction with

The Prins reaction with formaldehyde, acetic acid, acetic anhydride, and camphene gives the useful alcohol, 8-acetoxymethyl camphene, which has a patchouli-like odor (83). Oxidation of the alcohol to the corresponding aldehyde also gives a useful iatermediate compound, which is used to synthesize the sandalwood compound dihydo- P-santalol. 

Dioxanes can be efficiently synthesized from styrenes using formalin as the formaldehyde source (Prins reaction) with triflic acid as catalyst717 [Eq. (5.267)]. 

Some data have been reported for another reaction of formaldehyde, the Prins reaction, with a-methylstyrene. With water or 40 60 watei dioxane mixture as solvent, the reaction was reported to be first order kinetically in each reactant. A direct relation between the log of the rate coefficient and the acidity function Hq of the mineral acid catalyst was found [204]. 

Prins reactions with formaldehyde have been used to prepare prostaglandin intermediates. Reaction of norbomadiene with paraformaldehyde and formic acid at -80 °C gives (6) in 67% yield (equation 3). Reaction of unsaturated lactone (7) with formaldehyde in acetic acid at 60-80 C gives prostaglandin intermediate (8) in 75-85% yield (equation 4). Addition of protonated formaldehyde occurs from the less-hindered face of the double bond followed by trans addition of acetate to the carbocation. 

The Prins reaction with formaldehyde is a well-known route to prostaglandins using bicyclic lactone 3 as a precursor. One synthesis of this lactone14 started this sequence with a Prins reaction. Treatment of norbomadiene with paraformaldehyde in the presence of formic acid produced a mixture of epimeric diformates in 67% yield which were transformed in several steps into lactone 3. A second synthesis starts with the unsaturated bicyclic lactone which undergoes attack by the oxonium ion both regio- and stereoselectively from the less hindered face of the double bond, trims Addition of the nucleophilic acetate generates the lactone 3 as the bisacetate derivative15. 

Dioxanes can also be produced by the acid-catalysed condensation of alkenes with aldehydes, preferably with formaldehydes Prins reaction) ... 

The products of the Prins reaction with rubbers are thermoplastic polymers that possess fan-resistance to acids and bases. Free hydroxyl groups in the products are available for crosslinking with diisocyanates or by other means. The Prins reaction can be carried out directly on rubber latexes. It is also possible to just mill the rubber together with formaldehyde and then heat the resultant mixture in the presence of anhydrous metal chlorides to get similar results. ... 

Other acid-catalysed addition reactions include reaction with nitriles (Ritter reaction), formaldehyde (Prins reaction) and carbon monoxide and water (Koch reaction). These reactions are normally catalysed by concentrated sulphuric acid. Extensive isomerization occurs and may even lead to quaternary compounds of the type RC(CH3)XR where X is the new functional group introduced into the molecule. Homogeneous catalysts have been developed which give simpler products without extensive isomerization. 

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. 

An important synthetic process for forming a new carbon—carbon bond is the acid-catalyzed condensation of formaldehyde with olefins (Prins reaction) ... 

Uses ndReactions. Some of the principal uses for P-pinene are for manufacturing terpene resins and for thermal isomerization (pyrolysis) to myrcene. The resins are made by Lewis acid (usuaUy AlCl ) polymerization of P-pinene, either as a homopolymer or as a copolymer with other terpenes such as limonene. P-Pinene polymerizes much easier than a-pinene and the resins are usehil in pressure-sensitive adhesives, hot-melt adhesives and coatings, and elastomeric sealants. One of the first syntheses of a new fragrance chemical from turpentine sources used formaldehyde with P-pinene in a Prins reaction to produce the alcohol, Nopol (26) (59). 

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). 

Condensation of vinyl chloride with formaldehyde and HCl (Prins reaction) yields 3,3-dichloro-l-propanol [83682-72-8] and 2,3-dichloro-l-propanol [616-23-9]. The 1,1-addition of chloroform [67-66-3] as well as the addition of other polyhalogen compounds to vinyl chloride are cataly2ed by transition-metal complexes (58). In the presence of iron pentacarbonyl [13463-40-6] both bromoform [75-25-2] CHBr, and iodoform [75-47-8] CHl, add to vinyl chloride (59,60). Other useful products of vinyl chloride addition reactions include 2,2-di luoro-4-chloro-l,3-dioxolane [162970-83-4] (61), 2-chloro-l-propanol [78-89-7] (62), 2-chloropropionaldehyde [683-50-1] (63), 4-nitrophenyl-p,p-dichloroethyl ketone [31689-13-1] (64), and p,p-dichloroethyl phenyl sulfone [3123-10-2] (65). 

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 ... 

Terminal olefins such as 1476 react in an unusual Prins reaction [33] with formaldehyde in F3CC02H/Me3SiCl 14 to give in ca 75-90% yield a mixture of the cis/ trans 3,4-disubstituted tetrahydrofurans 1477 and 1478 [34] (Scheme 9.19). 

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. 

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. 

The microenvironmental effect of various sulfonated polystyrene beads was studied using the Prins reaction as a probe.372 Reaction rates were found to be lower when carbomethoxy or carbobutoxy neighboring groups were present compared to phenyl. A less ionic microenvironment appears to allow for a higher concentration of styrene within the polymer and leads to an immediate reaction with protonated formaldehyde. 

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... 

Lithium aluminum hydride reduction of epiquinamine, as expected, afforded 3-epicinchonamine, mp 168°, [a]D +48° (EtOH), also obtainable along with cinchonamine by the sodium-ethanol reduction of apoquinamine (23). Finally, it was shown in 1945 that, on heating quinamine or dihydroquinamine above its melting point, formaldehyde was evolved, and this was taken as evidence for the presence of a 2-hydroxymethyl on an indole a-carbon (15). In the light of the true structure, the writer would like to suggest that this aldehyde is formed by pyrolysis of a 1,3-glycol, that is, a retro Prins reaction (25). 

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). 

In the Cannizzaro reaction (62), which involves self-condensation of aldehydes that have no a-hydrogen atoms, the nucleophile is represented best as a hydride ion in the Prins reaction (26), the nucleophile is an olefin in the aldol condensation (63) and reaction of methyl acetate with formaldehyde (62), the nucleophile is a methylene group a- to a... 

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