Matched case

Aliphatic, aromatic and vinylic aldehydes can be employed in this reaction with similar yields and enantioselectivities. When chiral aldehydes are utilized, excellent diastereoselectivity is obtained for matched cases, whereas mismatched cases yield products with moderate to good diastereoselectivity (Scheme 9.13a) [67]. The limitation of the methodology is that only terminal vinylepoxides can be obtained. 

Early on, Shennan33 in 1973 and later Armstrong and Doll34 in 1975 found strong positive correlations between international kidney cancer rates and coffee consumption. However, in a matched case-control study... 

Consequently only second-order processes employing one e- and two o-waves may occur and the second conclusion of the last paragraph applies beyond the noncritical phase-matched case. 

Bradbury et al. (2004), however, recently reanalyzed the relation between tamoxifen and cataracts and described it as a null association, They used a nested, matched, case-control study design and data collected in the General Practice Research Database. They identified all women 30-79 years old who were diagnosed with breast cancer and treated with tamoxifen within 6 months, or with bladder cancer, colorectal cancer, or nonmelanoma skin cancer between January 1991 and December i999. From this population they identified all newly diagnosed cases of cataract and matched four female controls to each case on age, index date, and study entry data. They assessed the risk of cataracts for current, past, and sometime users of tamoxifen... 

Double stereodifferentiation This refers to the addition of a chiral enolate or allyl metal reagent to a chiral aldehyde. Enhanced stereoselectivity can be obtained when the aldehyde and reagent exhibit complementary facile preference (matched case). Conversely, diminished results might be observed when their facial preference is opposed (mismatched pair). 

Scheme 3 39 shows the reaction of boron enolates 106 and 108 with chiral aldehydes (2R,4S)- and (2S,4R)-96. In the matched case, lactone 3,4-anti-101 is obtained with very high ee.67... 

For applications in total synthesis this method was also thought to be applicable to chiral aldehydes, leading to matched and mismatched situations. Therefore, vinylogous ketene acetal 40 was put to reaction with chiral aldehyde 44 and both enantiomers of Carreira s catalyst. Reaction of aldehyde 44 with the (S)-Tol-BINAL-CuF catalyst (matched case) produced only one diastereomeric... 

By contrast, lithium enolates derived from tertiary amides do react with oxiranes The diastereoselectivity in the reaction of simple amide enolates with terminal oxiranes has been addressed and found to be low (Scheme 45). The chiral bicyclic amide enolate 99 reacts with a good diastereoselectivity with ethylene oxide . The reaction of the chiral amide enolate 100 with the chiral oxiranes 101 and 102 occurs with a good diastereoselectivity (in the matched case ) interestingly, the stereochemical course is opposite to the one observed with alkyl iodides. The same reversal is found in the reaction of the amide enolate 103. By contrast, this reversal in diastereoselectivity compared to alkyl iodides was not found in the reaction of the hthium enolate 104 with the chiral oxiranes 105 and 106 °. It should be noted that a strong matched/mismatched effect occurs for enolates 100 and 103 with chiral oxiranes, and excellent diastereoselec-tivities can be achieved. 

One common use of SHG is to convert the output of a fixed-frequency laser into a different spectral region. For example, the Nd-YAG laser operates in the near IR at a wavelength of 1,064 nm, while SHG is routinely used to convert the wavelength of the radiation to 532 nm. For x processes, the conversion efficiency can be up to 30% for phase-matched case with a nanosecond laser pulse. 

Double asymmetric induction is observed30 in the alkylation of 3-(2-hydroxyalkyl)-substituted 4,5-dihydroisoxazoles, e.g., 12. The stereoselectivity is controlled by both the C4-substituent and the exocyclic stereocenter. Thus, in the matched case, alkylation of the chelated Z-azaenolate occurs preferentially anti to the C4-substituent and the phenyl group. 

Consequently, matched/mismatched cases [25] can result, and indeed our investigations on cooperative effects of stereogenic elements in such systems revealed 9 be the matched case and 23 (which is also easily prepared by following a directed deprotonation-silylation-deprotonation-trapping-desilylation sequence [11]) to be the mismatched case in diethylzinc additions to aldehydes [26]. Later, these investigations were extended to more complex systems such as 24 [27], but ferrocene 9 still remains superior to all other compounds. 

In a related study, a matched case-control epidemiologic study to determine if chronic exposure to HDl resulted in an added decline in respiratory function above what is expected from aging alone was undertaken again at a plant in Freeport, Texas from 1988 to 1991 (see Shepperly and Hathaway 1991). 

For alkenylmetals bearing two stereocenters at both the allylic and homoallylic positions, two situations have to be distinguished depending on their relative influence (matched or mismatched) with respect to the stereochemical outcome of the allylzincation. Not surprisingly, in the matched case, as illustrated for substrate 232, the diastereoselectivity was excellent and 233 was obtained as a single diastereomer. The allyl moiety was delivered anti to both the allylic and homoallylic substituents in the chelated allyl alkenylzinc species (equation 113). 

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