Wittig Reaction catalytic

While being widely used for alkene synthesis, it is noteworthy that, as a stoichiometric transformation, Wittig reaction generates extensive waste due to the high mass of phosphine oxide side product which is not always easily separable from the desired product. While Wittig reaction catalytic in phosphine is merging [15], the establishment of fully compatible catalytic olelination processes is yet to be seen. 

The Corey process is also useful for the synthesis of PGs of the 1 and 3 series. Catalytic hydrogenation of (34) (see Fig. 5) with 5% Pd/C at — 15-20°C results in selective reduction of the 5,6-double bond. Subsequent transformations analogous to those in Figure 5 lead to PGE (9) and PGF (10). The key step for synthesis of the PG series is the Wittig reaction of (29) with the appropriate unsaturated CO-chain yUde (170). 

Whittlesey, Williams and co-workers fnrther developed the catalytic indirect Wittig reaction and fonnd that the more electron-rich NHC present in complex 18 provided a more reactive catalyst [8]. Catalyst 18 was used to convert benzyl alcohol 8 and phosphoninm ylide 19 into the product 20 under slightly milder reaction conditions and in a shorter time than in previous work (Scheme 11.4). Other C-C bond-forming reactions from alcohols using a borrowing hydrogen approach have been reported, with Peris and co-workers using Ir-NHC complexes for the C-3 alkylation of indoles with alcohols [9]. 

The Horner-Wittig reaction of a-phosphoryl sulphoxides 442, which are chemically stable, results in the formation of a, -unsaturated sulphoxides 443 in high yields (equation 264). The reaction has been found to be non-stereoselective, mixtures of E and Z isomers being formed from aldehydes and unsymmetrical ketones . In the case of aromatic aldehydes this reaction can also be advantageously performed in a two-phase catalytic system even without the usual PTC catalysts (Table 24). Intramolecular Horner-Wittig reaction of a-phosphoryl-5-oxosulphoxides 444 leads to a, -unsaturated cyclic sulphoxides 445 (equation 265). Starting from optically active 0,0-... 

A challenging goal is the development of catalytic asymmetric induction processes. Denmark et al.48 have reported an asymmetric Wittig reaction using... 

A useful application of the silver-mediated additions is 1,3 -diene synthesis by three-carbon elongation of aldehydes [48,51,53]. The bimetallic reagent 3-trimethylsilyl-l-propenylzirco-nocene chloride (A Scheme 8.23) reacts with aldehydes under the influence of a catalytic amount of Ag+ to give the intermediate zirconocene-alkoxide B, which then undergoes a Peterson-type 1,4-elimination of TMS alkoxide to stereoselectively afford ( )-dienes (fc/Z > 96 4) (Scheme 8.23). A Wittig reaction yields the same products without stereoselectivity (ca. 1 1 mixtures of E- and Z-isomers). 

Alternatively, bromo trienyne 66, prepared by the Wittig reaction of TMS-capped propargyl ylide with , -5-bromo-2,4-pentadienal, could be coupled with dienyl zinc reagent 67, as illustrated in equation 3657. Subsequent desilylation followed by treatment with trimethyl aluminum in the presence of catalytic Cp2ZrCl2 afforded the alane of tetraenyne 68 which, on exposure to chloroformate, gave essentially all- polyene ester 69. 

Wittig reaction of azocine 214 with triphenylmethylenphosphane gives methylene derivative 215. In contrast, under Wolff-Kishner reaction conditions 214 was transformed into azocine 216a. Catalytic hydrogenation of the methylene... 

Only one nonazapteridine (pyrimido[4,5- ]-l,2,4-triazine) derivative has been synthesized by the methods covered in this section. Thus, the reaction of the 5-amino-l,2,4-triazine-6-carboxylate 128a with triphenylphosphine/hexa-chloroethane produced the iminophosphorane 133 which underwent aza-Wittig reaction in hot benzoyl chloride in the presence of catalytic 4-dimethylaminopyridine (DMAP) to give the oxazino[6,5-< ]-l,2,4-triazine 134 as shown in Scheme 22 <2003ARK98>, which, as discussed in Section 10.20.1, constitutes an addition to the 44 ring systems covered by the remit of this chapter that were known at the time of CHEC-II(1996) <1996CHEC-II(7)785>. 

Wittig reaction to give the desired Michael acceptor. A second catalytic conjugate addition using Josiphos or its enantiomer affords with excellent diastereoselectivities the syn- or awf/-l,3-dimethyl derivative. 

For example, see Johnson LaCount Tetrahedron 1960, 9, 130 Bestmann Kratzer Chem. Ber. 1962, 95, 1894. An arsenic ylide has been used in a catalytic version of the Wittig reaction that is. the R AsO product is constantly regenerated to produce more arsenic ylide Shi Wang Wang Huang J. Org. Chem. 1989, 54, 2027. 

DMA followed by sodium methoxide furnished ylide (479) which was immediately condensed with diethyl JV-(p-formylbenzoyl)-L-glutamate to afford (480). Catalytic hydrogenation gave the 5,6,7,8-tetrahydro derivative oxidation with hydrogen peroxide followed by hydrolysis of the ester groups then gave (478). This is the first report of the preparation and use of a pteridine ylide in the Wittig reaction. 

The two-step procedure that was followed used a Wittig reaction to form the carbon-carbon bond, then catalytic hydrogenation of the resulting alkene. 

PhLi gave the ylid from 55 and the Wittig reaction with 54 did indeed give Z-52. These days we should probably use catalytic OSO4 for the dihydroxylation but his mixtures [1. AgOAc, I2, HOAc, H2O, 2. KOH, EtOH] also gave the diol 51 and TsCl in pyridine gave the bis tosylate 50. This chemistry is explained in the workbook. 

Tellurium-Wittig reactions.1 The reaction of aldehydes with a-bromo esters or ketones, triphenyl phosphite, and a weak base in the presence of a catalytic amount of Bu2Te results in ct, l-unsaturated esters and ketones. The function of the triphenyl phosphite is the regeneration of Bu2Te from the dibutyl telluroxide formed in the... 

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