Frans-chalcone

In the presence of thiourea 121 (20mol% in toluene at 4°C/20°C), the aza-Michael addition [149-152] of 0-benzylhyroxylamine to numerous frans-chalcones bearing electron-rich and electron-deficient (hetero)aromahc subshtuents as well as aliphatic side chains provided the respective P-keto hydroxylamines 1-8 in moderate to very good yields (35-94%) and low to moderate (30-60%) ee values... 

Scheme 6.139 Typical products of the aza-Michael addition of O-benzylhydroxylamine to frans-chalcones under bifunctional 121 -catalysis.

Scheme 7.1 Asymmetric epoxidation of tra/rs-enals and frans-chalcone by OTMS diaryl prolinol/H202 and r-diphenyl prolinol/TBHP s tems, respectively.

The frans-chalcone (Aldrich Chemical Co., 13,612-3) should be finely ground for... 

To a 10-mL round-bottom flask, add 0.24 g of finely ground frans-chalcone, 0.15 g of ethyl acetoacetate, and 5 mL of absolute ethanol. Swirl the flask until all or most of the solid dissolves and place a boiling stone in the flask. Add 0.25 mL of 2.2M NaOH to the mixture. Attach a water-jacketed condenser to the round-bottom flask and heat the mixture to reflux using an aluminum block and hot plate. Once the mixture has been brought to a gentle boil, continue to reflux the mixture for at least... 

Indicate how you could synthesize frans-chalcone. (Hint Experiment 37)... 

The Corey-Chaykovsky reaction will be used to cyclopropanate your chalcone from Experiment 61. The reaction involves the reaction of trimethylsulfoxonium iodide and potassium fcrf-butoxide in anhydrous dimethylsulfoxide (DMSO). The reaction is stirred at room temperature for 1 hr. For example, frans-chalcone (1,3-diphenyl-2-propen-l-one) produces an 88% yield of the cyclopropanated product. You will analyze your product by NMR and infrared spectroscopy. 

The high electron-withdrawing nature of the metal carbonyl fragment in the a,3-unsaturated Fischer carbene complex 84 reasonably explains the observed 1,4-addition. It is interesting to point out that reactions of ortho-hthiated aryloxiranes with simple a,p-unsaturated carbonyl compounds (e.g., iraws-cinnamaldehyde and frans-chalcone) usually proceed via a regioselective 1,2- rather than a 1,4-addition to the carbonyl moiety (2006JOC3984). 

If you had obtained both the cis- and frans-chalcone products, and had purified them by recrystallization, how could you instantly know which one was cis and which one was trans without any further characterization ... 

Complex LSB 9 is readily prepared either by the reaction of La 0 Pr)3 with 3 equiv. of BINOL followed by the addition of NaO Bu (3 equiv.) or by the reaction of LaC vnHjO with sodium binaphthoxide. The complex 9 is stable to oxygen and moisture and has b n proven to be effective in the catalytic Michael reaction of various enones with either malonates or -keto esters. The Michael adducts with up to 92% ee were obtained in almost quantitative yield. Topical results with malonates are summarized in Table 8D.1 (Ln = lanthanide) [18]. In general, the use of THF as solvent gave the best results except for the case of the LSB-catalyzed reaction of frans-chalcone with dimethyl malonate, wherein the use of toluene was essential to give the adduct with good enantiomeric excess. The effects of the central metal (La, Pr, and Gd) on asynunetric induction were also examined in the same reaction, and LSB was found to be the best catalyst. 

Chiral crystals generated from non-chiral molecules have served as reactants for the performance of so-called absolute asymmetric synthesis. The chiral environments of such crystals exert asymmetric induction in photochemical, thermal and heterogeneous reactions [41]. Early reports on successful absolute asymmetric synthesis include the y-ray-induced isotactic polymerization of frans-frans-l,3-pentadiene in an all-frans perhydropheny-lene crystal by Farina et al. [42] and the gas-solid asymmetric bromination ofpjp -chmethyl chalcone, yielding the chiral dibromo compound, by Penzien and Schmidt [43]. These studies were followed by the 2n + 2n photodimerization reactions of non-chiral dienes, resulting in the formation of chiral cyclobutanes [44-48]. In recent years more than a dozen such syntheses have been reported. They include unimolecular di- r-methane rearrangements and the Nourish Type II photoreactions [49] of an achiral oxo- [50] and athio-amide [51] into optically active /Mactams, photo-isomerization of alkyl-cobalt complexes [52], asymmetric synthesis of two-component molecular crystals composed from achiral molecules [53] and, more recently, the conversion of non-chiral aldehydes into homochiral alcohols [54,55]. 

The aldol reaction (aldol condensation) is one of the fundamental reactions of organic chemistry because it leads to the formation of a new carbon-carbon bond (see Experiment [20] for a very similar example of the Qaisen-Schmidt type of aldol reaction). In this version, the condensation of 4-nitrobenzaldehyde (an aldehyde without an a-hydrogen atom) with acetophenone (a ketone) gives frans-4-nitrochalcone.The aldol condensation of the unsubstituted aromatic aldehyde, benzaldehyde with acetophenone, yields frans-l,3-diphenyl-2-propenone (PhCH CHCOPh), which has the common name, chalcone.Thus, the substituted derivatives of this system are known collectively as chalcones. 

Synthetic polypeptides were found, by Julia, to epoxidize a, i-unsaturated ketones with high enantioselectivity [12], The Julih process can be easily performed at O C, and using a triphasic system comprising of toluene, water and polyalanine in the presence of alkaline hydrogen peroxide, chalcone oxide was produced in 97% ee (Scheme 1.7). The Julia process has become the method of choice for the epoxidation of fran.y-l,3-diarylenones. However, this methodology is extremely substrate-specific, and enones with enolisable a-protons are usually poor substrates. 

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