Dibenzo-18-crown-6 ether phase transfer catalyst

Triorganotin fluorides can be prepared by the use of new fluorinating systems. 18-Crown-6 or dibenzo-24-crown-8 can act as solid-liquid phase transfer catalysts for CsF. Trialkyltin mercaptides can be fluorodestannylated by CsF in the presence of crown ethers or alkyl bromides358 ... 

The cocatalytic effects of pinacol in the phase transfer catalysis (PTC) of dihalocarbene additions to alkenes were noted by Dehmlow and co-workers who showed that pinacol accelerates the PTC deprotonation of substrates up to pKa 27.7 Dehmlow also studied the effects of various crown ethers as phase transfer catalysts in the addition of dibromocarbene to allylic bromides.8 In Dehmlow s study, elevated temperature (40°C) and dibenzo-18-crown-6 did not give the highest ratio of addition/substitution to allyl bromide. However, the submitters use of pinacol,... 

Both activation by Cr(CO)3 complexation and the use of phase-transfer conditions are necessary for success in the following synthesis. A cyclic bis-ether can easily be obtained from the o-dichlorobenzene complex 18a (Scheme 14). Indeed, reaction of 18a with Na[0(CH2)2]20H in (MeOCH2)20 and with Bu4NBr as a phase-transfer catalyst at 50 °C for 8 h, followed by decomplexation with I2 directly affords dibenzo-18-crown-6 35 in 27 % yield. Compound 34, which can also be converted into 35, can be obtained in 84 % yield by heating 18a, NaH, and diethylene glycol for 24 h in DME at 50 °C [19]. The authors demonstrated the potential of this synthesis by preparing different crown ethers with various heteroatoms. 

The type of phase-transfer catalyst plays a key role in the phase-transfer catalytic synthesis of l-bromo-1-chlorocyclopropanes, which are formed in good yields and with high selectivity if the reaction of dibromochloromethane with an alkene is performed using a crown ether (dibenzo-18-crown-6, " 3,5-di-fer/-butylbenzo-15-crown-5, " " 3,3, 5,5 -tetra-tert-butyldiben-zo-lS-crown-b ) or tetramethylammonium chloride.For the specific effect of the tetra-methylammonium chloride on the dichlorocyclopropanation of unconjugated dienes, see Section I.2.I.4.2.I.2., and some electrophilic alkenes, see Section I.2.I.4.2.I.8.2. The reason why these catalysts exhibit peculiar properties is not clear,other crown ethers behave like typical phase-transfer catalysts (Table 25). " ... 

Catalysts in reactions of carbanions and halocarbenes. M kosza and M. Ludwikow report that crown ethers, particularly dibenzo-18-crown-6 (1), can function as phase-transfer catalysts in two-phase reactions of carbanions and halocarbenes. An example is the reaction of diphenylacetonitrile (2), which contains an acidic hydrogen, with an alkyl halide in 50% aqueous NaOH ... 

Quaternary alkylammonium salts, tertiary amines, and crown ethers have all been utilized as catalysts in the reaction of hydroxide with chloroform to yield dichlorocarbene. The most commonly utilized catalyst has been benzyltriethylammonium chloride (see Sect. 1.7) but other quaternary ammonium chloride catalysts have proved effective. Cetyltrimethylammonium chloride and tricaprylmethylammonium chloride (Aliquat 336) have both been used effectively in the cyclopropanation of simple alkenes. The use of Z e a-hydroxyethyltrialkylammonium hydroxides as phase transfer catalysts results in increased regioselectivity in the addition of dichlorocarbene to olefins [12]. Crown ethers such as dibenzo and dicyclohexyl-18-crown-6 have both been utilized in place of quaternary ammonium compounds. 18-Crown-6 has also been used as a catalyst in the phase transfer thermal decomposition of sodium trichloroacetate to yield dichlorocarbene [13]. 

Sodium hydroxide 18-crown-6 poly ether c/5 -Thioenolethers from acetylene derivs. cf. 12, 653 dibenzo-18-crown-6 as phase transfer catalyst, at room temp., s. B. A. Trofimov, S. V. Amosova, and V. B. Nosyreva, Zh. Org. Khim. 12, 1366 (1976) C. A. 85,77785... 

The crown ether catalyzed phase transfer reductions which have been reported are similar to the quaternary ion catalyzed reactions in the sense that if the proper catalyst is chosen the reactions yield well but appear to offer no special advantage over more traditional reduction methodology. The dibenzo-18-crown-6 catalyzed sodium borohydride reduction of several ketones in boiling toluene (5 h reaction time) has been reported [7]. By this method, acetophenone, cyclohexanone and 2-heptanone were reduced in 49%, 50% and 41% yields respectively. 

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