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Side Chain Elaboration

An effective 10-step procedure leading to a25-OH side chain in 42% yield from the Ci9 steroid aldosterone has been accomplished [scheme The addition [Pg.35]

From the C21 steroid, pregnenolone, many excellent synthetic schemes to hydroxylated side chain derivatives have been developed. Direct condensation of the [Pg.35]

Another creative scheme which originates from pregnenolone [scheme (6)] utilizes vinyl magnesium bromide as the initial reactant and yields the corresponding [Pg.36]

By far the most widely used starting material for side chain elaboration schemes has been the C-22 aldehyde. This compound, readily obtained from the ozonolysis of sigmasterol i-ether or the 4-phenyl-l, 2,4-triazoline-3,5-dione (PTAD)-diene adduct of ergosterol has been modified in a number of ways. [Pg.36]

Reduction to the alcohol, tosylation and conversion to the C-22 iodo derivative provides the substrate for reaction with a-(dimethyl allyl) nickel bromide. This coupling reaction gives the desmosterol side chain directly [scheme (7)]  [Pg.37]


Folate analogues continue to have importance in chemotherapy, especially heterocyclic analogues other than pteridines which are covered in Chapters 10.15-10.17 and 10.19. 1,3-Dimethyllumazine analogues of folates for use as model compounds have been prepared by side-chain elaboration of 6-bromomethyl-l,3-dimethyllumazine (Scheme 34) <1996JHC341>. More notable in this work, however, was the synthesis of the bromomethyl precursor itself in addition to routine bromination of the 6-methyllumazine 175 prepared by condensation of dihydroxyacetone with 5,6-diamino-l,3-dimethyluracil, a cycloaddition reaction between trimethylsilyl enol ethers and the pyrimidyl bisimine 177, via cycloadducts such as 176, afforded substituted pteridines in moderate to good yields. [Pg.948]

Methylquinazolin-4(3i/)-one is converted into the dianion 1 using uncomplexed butyl-lithium. Subsequent condensations of 1 with alkyl halides, ketones and aldehydes result in selective modification of the original methyl group to form derivatives 2, This reaction represents a direct, general method for side-chain elaboration of 2-alkylquinazolin-4(3//)-ones. ... [Pg.137]

The vinyltin moiety can form part of a diene system and undergo coupling with a dienyl iodide to form a tetraene [23] (Scheme 4-3). Crisp and Glink [24] have carried out a number of couplings directed towards -amino acid side-chain elaboration steps and observed the occurrence of ipso-substitution as a side reaction. [Pg.96]

The africanane sesquiterpenes have an interesting rearranged guaiane-type carbon skeleton, which can be obtained from (/ )-pulegone, ring contraction, side chain elaboration, and RCM (Scheme 24) [59]. [Pg.439]


See other pages where Side Chain Elaboration is mentioned: [Pg.199]    [Pg.51]    [Pg.218]    [Pg.196]    [Pg.196]    [Pg.321]    [Pg.108]    [Pg.20]    [Pg.34]    [Pg.35]    [Pg.219]    [Pg.100]    [Pg.123]    [Pg.192]    [Pg.28]    [Pg.11]    [Pg.35]    [Pg.435]    [Pg.196]    [Pg.380]    [Pg.380]    [Pg.14]    [Pg.198]    [Pg.207]   


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Elaboration

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