Enol trichloroacetate

The complex (A,A)-(ebthi)TiCl(OMe) has been synthesized from the corresponding titanium dichloride. This compound catalyzes the asymmetric aldol reaction of enol trichloroacetate of cyclohexanone with aromatic aldehydes with the result that the optically active syn-aldol adduct is obtained with up to 91% ee.1664... 

Aldol reactions. A combination of AgOTf, (/ )-BINAP, and RjSnOMe promotes a diastereoselective-enantioselective aldol reaction of enol trichloroacetates with aldehydes. ... 

To use less tin in the reaction, a catalytic amount of tin methox-ide has been used with enol trichloroacetates in the presence of BDSTAP-AgOTf complex (eq 62). These modifications appeared to be as effective as the original version. ... 

Scheme 3-204. Bu2Sn(OMe)2 catalyzed aldol reaction of enol trichloroacetates.

Geranyl chloride can be prepared from geraniol by the careful use of triphenylphosphine in carbon tetrachloride. Tris(dimethylamino)phosphine reacts with carbon tetrachloride to form the complex (42) which can be used to form the enol esters (43) from acid anhydrides. Similarly, aldehydes form the alkenes (44), and esters or amides of trichloroacetic acid are converted to glycidic esters. ... 

Besides the silyl enolate-mediated aldol reactions, organotin(IY) enolates are also versatile nucleophiles toward various aldehydes in the absence or presence of Lewis acid.60 However, this reaction requires a stoichiometric amount of the toxic trialkyl tin compound, which may limit its application. Yanagisawa et al.61 found that in the presence of one equivalent of methanol, the aldol reaction of an aldehyde with a cyclohexenol trichloroacetate proceeds readily at 20°C, providing the aldol product with more than 70% yield. They thus carried out the asymmetric version of this reaction using a BINAP silver(I) complex as chiral catalyst (Scheme 3-34). As shown in Table 3-8, the Sn(IY)-mediated aldol reaction results in a good diastereoselectivity (,anti/syn ratio) and also high enantioselectivity for the major component. 

Since the use of stoichiometric amounts of organostannane is unfavorable for the environment, they have established reaction conditions for a process that is catalytic in organostannane. Thus, the reaction with an alkenyl trichloroacetate as the precursor of the tin enolate in the presence of the catalytic amount of Me3SnOMe and the appropriate aldehydes afforded the corresponding aldol adducts with high enantio-and diastereoselectivities (Table 9.8).17 However, when the aliphatic aldehydes were used as substrates, the reaction did not take place at all. The proposed catalytic cycle is shown in Figure 9.3. It was also demonstrated that this catalytic system could be applied using a [3-lactone compound as an alkenyl trichloroacetate equivalent to... 

As resolution procedures are often tedious, and asymmetric synthesis provides chiral products with only limited enantiomeric excess, it seems an obvious strategy to use an enantiomerically pure material from the chiral pool to construct chiral ferrocenes by incorporating these compounds in the final product. As such chiral materials, cheap terpenes (menthone, a- and -pinene, and camphor) were chosen. The reaction of ferrocene with carbonyl compounds under acidic conditions is a very convenient way to obtain directly a-ferrocenylalkyl carbocations. The starting materials were therefore converted to aldehydes or their enol ethers (menthone and camphor are too sterically hindered and do not react with ferrocene). Joint dissolution of the aldehydes and ferrocene in trifluoroacetic acid or in the trichloroacetic acid/ fluorosulfonic acid system gives a-ferrocenylalkyl carbocations, which can either... 

The biomimetic total synthesis of (+)-20-epiervatamine was accomplished by J. Bosch et al. The authors used the addition of 2-acetylindole enolate to a 3-acylpyridinium salt as akey step to connect the two main fragments. The in situ formed 1,4-dihydropyridine was trapped with trichloroacetic anhydride to afford the corresponding trichloroacetyl-substituted 1,4-dihydropyridine derivative. The conversion of the trichloroacetyl group to a methyl ester was achieved by treatment with sodium methoxide. This transformation can be regarded as the second step of the haloform reaction. 

Reformatsky reagent Ethyl trichloroacetate reacts with zinc in THF at —15° to form a stable chlorozinc enolate (1). This reagent can be condensed with a number of... 

Using bromodichloromethyl(phenyl)mercury, vinyl acetate afforded 2-acetoxy-l,l-dichlo-rocyclopropane (1, 85%), dichlorocyclopropanation of other aldehyde enol esters would also be expected. The cyclopropane 1 ( 10%) together with 2-acetoxy-l,l,l-trichloropropane (2,10%) were formed when the dichlorocarbene was generated from sodium trichloroacetate, the chain product 2 results from the reaction of the trichloromethyl anion (for the mechanism, see ref 197). These reactions are described in Houben-Weyl, Vol. 4/3, pp 177-178. Under phase-transfer catalytic conditions (CHClj/base/PTC), with a typical catalyst such as benzyl-triethylammonium chloride, vinyl acetate gave 2 (65%) only (Houben-Weyl, Vol.E19b, ppl550-1551). 

Pummerer rearrangement of the Michael adducts would produce reactive sul-fenium ion intermediates 49 susceptible to a second nucleophile attack intramolecular trapping by the enol oxygen would then give the cyclized products (50). This two-step transformation was achieved directly in good yield by treatment of 48 with trichloroacetic acid and acetic anhydride in refluxing toluene. MCPBA oxidation of sulfide 50 followed by spontaneous elimination afforded furan 51 in good overall yield (Table 6). 

Methanol is oxidized to formate ions, acetone and acetaldehyde to acetate species. An enolic form of adsorbed acetone is seen, which accounts for rapid isotopic exchange of -OH. On O2 adsorption two bands at 1155 and 1020 cm are formed,which are however not assigned. Mixtures of CO plus O2 lead to the obvious formation of carbonates and bicarbonates. CO interaction with presorbed NH3 forms carbamate species. Oxidizing properties of the surface are shown by the reaction of trichloroacetone to trichloroacetate species. Nitriles are, however, hydrolysed to acetimidate species R-CNH . Similar reactions with surface -OH are shown by ethyl and phenyl isocyanate, which form urethanes by reaction with isolated -OH groups, and 1,3-diethylurea with -OH pairs. Reaction with surface -OH is also shown by trimethylchlorosilane, which, however, harshly attacks the surface and forms silicone species. ... 

In analogy t 0 the Cu(II) complex systems, the silver(I) -catalyzed aldol reaction is also proposed to proceed smoothly through a Lewis acidic activation of carbonyl compounds. Since Ito and co-workers reported the first example of the asymmetric aldol reaction of tosylmethyl isocyanide and aldehydes in the presence of a chiral silver(I)-phosphine complex (99,100), the catalyst systems of sil-ver(I) and chiral phosphines have been applied successfully in the aldol reaction of tin enolates and aldehydes (101), Mukaiyama aldol reaction (102), and aldol reaction of alkenyl trichloroacetates and aldehydes (103). In the Ag(I)-disphosphine complex catalyzed aldol reaction, Momiyama and Yamamoto have also examined an aldol-type reaction of tin enolates and nitrosobenzene with different silver-phosphine complexes (Scheme 15). The catalytic activity and enantioselectivity of AgOTfi(f )-BINAP (2 1) complex that a metal center coordinated to one phosphine and triflate were relay on solvent effect dramatically (Scheme) (104). One catalyst system solves two problems for the synthesis of different O- and AT-nitroso aldol adducts under controlled conditions. 

An alternative approach condensed 6.99 with the magnesium enolate of methyl trichloroacetate, 6.108. This reaction gave a 70 30 mixture of 3R,4S 3S,4S 6.109. Separation of the diastereomers and catalytic hydrogenation led to hydrogenolysis of the a-chloro moiety to give 3SAS-6.I10 in 90% yield. 

B) and methyl trichloroacetate. Then, the tin enolate (B) is allowed to add to an aldehyde under the influence of a BINAP-AgOTf complex to give a tin alkoxide of nonracemic aldol adduct (C). Finally, methanolysis of the alkoxide (C) gives the desired product (D) and regenerates the tin methoxide. 

The successful use of the silver complex formed from an iso-leucine-derived phosphine (L2 in Scheme 11.4) as catalyst for the multicomponent Mannich reaction of silyl enol ethers 10 with in situ formed aliphatic imines allowed its application in the enantioselective synthesis of the alkaloid sedamine (56% yield, 98% ee) [17]. Also cyclic and acyclic alkenyl trichloroacetates (10, Z = EtOCO) can be used in the reaction with ethyl glyoxylate and diverse aniline derivatives 11 catalyzed by... 

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