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Threitol derivatives

The initial investigation focused on the use of threitol-derived auxiliaries with various substituent groups on the dioxolane ring (Table 3.3). However, it became evident that the oxygen atoms in the substituents had a detrimental effect on selectivity. Comparison of the diastereoselectivities for the ketals 69-71, which contain Lewis basic sites in the substituents at the 1 and 2 positions, with those from simpler diol derived ketals 72-74 demonstrates the conflicting effects of numerous coordination sites. The simpler, diol-derived ketals provide superior results compared to the threitol derived ketals. The highest diastereoselectivity is observed in the case of the 1,2-diphenyl ethane-1,2-diol derived ketal 74. [Pg.108]

Among the 1,4-di-O-substituted-L-threitol derivatives (Figure 14a) the one that has found most use in chiral crown ether synthesis is the 1,4-dibenzyl ether. Not only has it provided (88, 106, 107) a ready entry into the chiral tetrasub-stituted 18-crown-6 derivatives ll-31 to ll-34, but it has also proved to be a usehil chiral precursor for the preparation of chiral disubstituted 9-crown-3 (107), 12-crown-4 (108), 15-crown-5 (108), and 18-crown-6 (109) derivatives l-57, l-58, l-59, and l-60, respectively. In the preparation of l-S8 the base-promoted cyclization with triethylene glycol ditosylate is best carried out (108) with a... [Pg.236]

Scheme 1.6. Regio- and diastereoselective double Diels-Alder addition to Cgo using a threitol derivative as imprinting template. Scheme 1.6. Regio- and diastereoselective double Diels-Alder addition to Cgo using a threitol derivative as imprinting template.
The study of chiral 1,4-threitol-derived dioxolanes was also extended to a series of medium and large ring olefins. Very high diastereoselectivities were obtained for both (Z)- and ( -configurated olefins in ring sizes of five to sixteen63. [Pg.991]

Synthesis from L-threitol The L-threitol derivative 24, obtained from D-(-)-diethyl tartarate in three steps and 90% overall yield, was used as a starting material for the synthesis of nectrisine (1) (Scheme 5). " Swern oxidation of 24 produced the L-threose derivative 25, which was transformed into the aminonitrile 26 in 96% overall yield from 24, as an inseparable diastereomeric mixture. Removal of the silyl protecting group from 26 followed by oxidation of the resulting primary hydroxyl group with TPAP afforded the lactam 27, which was treated with sodium methoxide to produce the methyl ester 28 in 62% yield from 26. Lithium borohydride reduction of 28 afforded a chromatographically separable mixture of the lactams 29 and 30 in a ratio of 56 44 and 87% total yield. Silylation... [Pg.14]

Anisomycin was also prepared from L-threitol derivative 51 in 17-20% overall yield (Scheme 6). Swern oxidation of 51 ° followed by Wittig methylenation, acidic... [Pg.49]

The first total synthesis of the enanfiomerically pure (+)-form 1 starting tfom L-threitol led to the assignment of the absolute configuration for the natural (-)-codonopsinine as 3 (Schemes The L-threitol derivative 7, obtained from L-tartaric acid in 55% overall... [Pg.61]

The versatility of 330b is demonstrated by the systematic transformation of 330b into a number of protected L-threitol derivatives. Facile sodium borohydride reduction in aqueous ethanol followed by DIBAL reductive cleavage of the resulting diol 383 provides (2S,3S)-2-O-benzyl-L-threitol (384) (the enantiomer of 352) in good yield. In fact, this two-step procedure is preferred, because it is more practical than one-step reductive cleavage (LiAlH4-... [Pg.375]

Intramolecular iodoamidation of pentenetriol derivative 52, obtained from L-threitol derivative 51, was used to prepare (-)-anisomycin in 17 20% overall yield (Scheme 6) [61]. Oxidation of 51 [62], followed by methylenation, acid hydrolysis, and protection with CCI3CN gave the olefin 52, whose reaction with iodine in the presence of sodium bicarbonate gave a 4.5 1 mixture of 53 and 54. Hydrolysis of the mixture, followed by N-protection with B0C2O afforded a 12 1 mixture of 55 and 56. On the other hand, when 52 was reacted with iodine monobromide in the presence of potassium carbonate, compound 53 only was obtained that could be transformed into a 37 1 mix-... [Pg.257]

A practical synthesis of l,2- -lsopropylidene-L-glyceraldehyde (8) from L-tartarlc acid (9) (Scheme 3) has been described, and Involves the intermediacy of the L-threitol derivative (10). ... [Pg.164]

Transmetallation can be employed in order to avoid the use of strongly basic conditions. One such variant is the [2,3]-Wittig-Still rearrangement wherein stannyl ethers can be converted to homoallylic alcohols. Several examples of this tranformation in the synthesis of amino acid components of bioactive polyoxins have been reported by Ghosh. In their synthesis of 5-0-carbomylpolyoxamic acid, a bioactive amino acid nucleoside, E and Z-allylic stannyl ethers, such as 45, derived from an isopropylidene L-threitol derivative, were subjected to the [2,3]-Wittig-Still rearrangement. [Pg.247]

Two efficient new syntheses of 1-deoxy-D-r/treo-pentulose (2), both starting from known D-threitol derivatives and employing a Grignard addition to 4-0-benzyl-2,3-0-isopropylidene-D-threose (1), have been published. Compound 2 exists mostly as the acyclic ketone in neutral aqueous solution, but forms a dimeric anhydride in acidic media (see Chapter 22 for crystal structure). [2,3- C2]-Labelled 2, which was similarly obtained from [l,2- C2]-labelled 1, has been used for investigating the biosynthesis of vitamins Bi and... [Pg.176]

The helical polymer 15 has been prepared from the D-mannitol derivative 16 and a diboronic acid. Similar polymers can be obtained using d- and L-threitol derivatives. In a related way condensation of the same diboronic acid with saccharides affords saccharide-containing polymers which display CD spectroscopic properties reflecting the chirality of the saccharides. ... [Pg.229]


See other pages where Threitol derivatives is mentioned: [Pg.156]    [Pg.13]    [Pg.51]    [Pg.131]    [Pg.150]    [Pg.101]    [Pg.679]    [Pg.150]    [Pg.640]    [Pg.990]    [Pg.100]    [Pg.102]    [Pg.209]    [Pg.284]    [Pg.385]    [Pg.51]    [Pg.586]   
See also in sourсe #XX -- [ Pg.101 ]




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