Biphasic catalysts allylation reactions

In water-heptane biphasic systems, allylic alcohols underwent rearrangement to the corresponding carbonyl compounds with a catalyst prepared in situ from RhCU.aq and TPPTS. The reactions proceeded very fast (TOP up to 2500 h ) and in most cases provided the carbonyl products quantitatively. The industrially interesting geraniol was isomerized mostly to citronelM, albeit octatrienes and tricyclene were also produced. With an increase of the pH of the aqueous phase the yield of isomerization decreased somewhat (from 48 % to 40 %), however the selectivity towards the... 

B. Potassium allyl- and crotyltrifluoroborates undergo addition to aldehydes in biphasic media as well as water to provide homoallylic alcohol in high yields (>94%) and excellent diastereoselectivity (dr >98 2). The presence of a phase-transfer catalyst (e.g., B114NI) significantly accelerates the rate of reaction, whereas adding fluoride ion retards the reaction (Eq. 8.70).165 The method was applied to the asymmetric total synthesis of the antiobesity agent tetrahydrolipstatin (orlistat).166... 

In the carbonylation of allyl halides the highly toxic [Ni(CO)4] catalyst could be replaced by [Ni(CN)2], which yielded [Ni(CN)(CO)jr under the reaction conditions [17]. The cyanotricarbonylnickel(0) anion is a versatile catalyst of carbonylations under phase transfer conditions [18], however, hydroxycarbonylation of allyl chloride proceeds effectively without PT catalysts in a genuine biphasic system, as well. 

This screening concept was also applied to liquid/liquid systems. As a test reaction, the isomerization of allylic alcohols to carbonyls with water-soluble catalysts in a biphasic heptane/water system was chosen [109,113]. The catalysts (metal precursor, Rh, Ru, Pd, Ni ligands, sulfonated phosphane or disphosphane ligands) were injected the liquid carrier 2 (water). The substrates (different allylic alcohols) were injected into liquid carrier 1 (heptane) ... 

Most examples describe catalyzed biphasic reactions taking the extra advantage of product isolation and catalyst recycling. De Bellefon et al. [211] published one of the first examples of biphasic reactions performed in a microreactor. The isomerization of allylic alcohols to carbonyl compounds was conducted in a liquid-liquid system using a micromixer combined with a microchannel tube. As there are limited examples of biphasic isomerization reactions, the authors were interested on... 

The biphasic allylic alkylation of ethylcinnamyl carbonate with ethyl acetoacetate has been studied in [C4Ciim]Cl-methylcyclohexane with PdCF/TPPTS as catalyst.[I2S Relative to the same reaction under aqueous... 

C-C coupling reactions include Pd-catalyzed carbonylations as well as Heck reactions. Biphasic operations are reported as being particularly efficient. Allyl and benzyl chlorides have been converted in two-phase systems to the corresponding acids with or without phase-transfer catalysts (eq. (6)) [154-157, 237]. 

Several of the factors of Figure 3 controlling the activity and selectivity of the biphasic selective hydrogenation of ,/ -unsaturated aldehydes to allylic alcohols, for instance, 3-methyl-2-butenaldehyde to 3-methyl-2-buten-l-ol (Eq. 11) with rutheni-um-sulfonated phosphine catalysts were investigated [11], such as the effect of agitation speed and the influence of aldehyde, ligand, and metal concentrations. Under optimized reaction conditions, where gas-liquid mass transfer was not rate-determining, the kinetic equation (Eq. 12) was found to apply. A zero-order dependence with respect to the concentration of the ,/i-unsaturated aldehyde was found. 

In the deprotection of phenylacetic allyl esters over Pd(OAc)2/TPPTS catalysts, it was noted that the reaction medium plays a role in determining reaction selectivity. The reaction is shown below in Eq. (1). When the reaction is performed homogeneously in CH3CN/H20 as the solvent, the allyl substituents with Rt = R2 = H Rj = Ph, R2 = H Rj = R2 = Me are all substituted [20, 21] the first in the series is the fastest to react. In contrast, when the reaction takes place under biphasic conditions in C3H7CN/H20, only the simple allyl ester, R, — R2 — H, is cleaved. When two allylic esters are incorporated into a single molecule the allyl ester can be selectively substituted under two-phase reaction conditions. 

---