In 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. 

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... 

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

Snider has found dialkyl aluminium halides to be excellent catalysts for this reaction and they can be used to stop the reaction after the first step. This is a real advance in the Prins reaction that otherwise tends to give a mixture of products by multiple addition of the aldehyde and intervention by various nucleophiles. A simple example is the addition of formaldehyde to the terpene limonene 208 catalysed by BF3. A single monoadduct 210 is formed in good yield.34 This must be a Lewis acid catalysed carbonyl ene reaction on the external double bond 209. Notice the excellent chemoselectivity in that the internal alkene is not attacked and the excellent regioselectivity in that hydrogen atoms at four other sites might have taken part in the reaction, but do not. 

Lewis acid catalyzed ene reactions are stepwise, rather than concerted, but that the intermediate bears more resemblance to a ir-complex than to the open carbocation intermediate in the Prins reaction. 

Cuprous chloride tends to form water-soluble complexes with lower olefins and acts as an IPTC catalyst, e.g., in the two-phase hydrolysis of alkyl chlorides to alcohols with sodium carboxylate solution [10,151] and in the Prins reactions between 1-alkenes and aqueous formaldehyde in the presence of HCl to form 1,3-glycols [10]. Similarly, water-soluble rhodium-based catalysts (4-diphenylphosphinobenzoic acid and tri-Cs-io-alkylmethylam-monium chlorides) were used as IPTC catalysts for the hydroformylation of hexene, dodecene, and hexadecene to produce aldehydes for the fine chemicals market [152]. Palladium diphenyl(potassium sulfonatobenzyl)phosphine and its oxide complexes catalyzed the IPTC dehalogenation reactions of allyl and benzyl halides [153]. Allylic substrates such as cinnamyl ethyl carbonate and nucleophiles such as ethyl acetoactate and acetyl acetone catalyzed by a water-soluble bis(dibenzylideneacetone)palladium or palladium complex of sulfonated triphenylphosphine gave regio- and stereo-specific alkylation products in quantitative yields [154]. Ito et al. used a self-assembled nanocage as an IPTC catalyst for the Wacker oxidation of styrene catalyzed by (en)Pd(N03) [155]. 

Miscellaneous.—Extended Huckel MO calculations have been used to provide the electronic energy levels and charge distributions of cephalosporin-and penicillin-derived structures. Non-empirical SCF-MO calculations suggest that the protonated oxetan (4) is the most stable of the five possible intermediates of formula [C3H70]+ in the Prins reaction between ethylene and formaldehyde. Experimental support is provided by similar reactions of a-methylstyrene. 

Se02 catalyzes the oxidation of olefins to allylic alcohols in the presence of an oxygen donor such as cBuOOH as a co-substrate. The mechanism is probably concerted (a) as in the Prins reaction of aldehydes with aikenes (b). 

The implementation of the two mechanisms corresponds to the experimental data on a stereoselective Prins reaction for a series of cycloalkenes [15], However, the role of formaldehyde oligomers in the Prins reaction and its reactivity in addition to the alkenes with various structures are still poorly described. 

Talipov, R. F. (1984). DUiydio- and alkeniltetrahydropyrans in the Prins Reaction. Ph.D. Thesis. Bashkir State University, Russia. 

In addition to the iminium-salt-based chemistry and to cross-coupling processes, aqueous formaldehyde can also be used as the carbonylated substrate in the Prins reaction, an intermolecular ene-type acid-catalyzed reaction with alkenes providing 1,3-dioxanes (Adams and Bhatnagar, 1977). 

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