Aldols structure

O. Oddo discussed this reaction as an example of what he calls mesoidria, i.e., mesokydry. L. Lendle, and G. Schick inferred that barium phosphite exists in isomeric forms because of the difference in the reducing properties of the phosphites prepared at high and at low temp. The low temp, form was said to be the most active, and to it was attributed an aldolic structure while the enolic structure was assigned to the less active form prepared at the high temp. ... 

A few years ago, Riant and co-workers had already presented a fine example of a copper(l)-catalyzed domino silylative aldol reaction. The stereochemical outcome was controlled by the use of a chiral oxazolidinone auxiliary attached to a Michael acceptor (Scheme 37) [88], The copper(l)-enolate formed by the conjugate silylation of acryloyloxazolidinone 143 was trapped with different aldehydes to yield aldol structures 145d and 145g-i diastereoselectively (Scheme 37, upper). 

Figure 1 A Retrosynthetic Scheme to the Target Aldol Structures...

As described above, a novel preparation of homochiral mono-, di-, as well as trifluoromethylated aldol structures starting from the readily available chiral pool compound, D-glucose, has been demonstrated. Further synthetic utilization of optically active cyclic materials as well as investigation of the similar route with different sugars is under way in our laboratory. 

Write the structure of the aldol condensation product of eacfT... 

Give the structure of the mixed aldol condensation product of... 

Write structural formulas corresponding to the intermediates formed in the con (jugate addition step and in the aldol addition step ... 

Give the structure of the product denved by intramolecular aldol condensation of the keto aldehyde shown... 

Katada rearrangement, 3, 289 synthesis, 3, 305 Lumazine, 7-methyl-aldol-type reactions, 3, 302 synthesis, 3, 311 Lumazine, 8-methyl-structure, 3, 277... 

Pteridine, 4-imino-1 -methyl-1,4-dihydro-basicity, 3, 270 Pteridine, 7-methoxy-synthesis, 3, 297 Pteridine, 2-methyl- H NMR, 3, 285 reactions, 3, 288 structure, 3, 266 Pteridine, 4-methyl-Gabriel s synthesis, 3, 309 H NMR, 3, 285 reactions, 3, 288 structure, 3, 266 Pteridine, 6-methyl-bromination, 3, 301 structure, 3, 266 synthesis, 3, 312 Pteridine, 7-methyl-aldol-type condensation, 3, 302 bromination, 3, 301 H NMR, 3, 285 structure, 3, 266 synthesis, 3, 312 Pteridine, 2-methylamino-solubility, 3, 271 Pteridine, 2-methyl-3,4-dihydro-striicture, 3, 279 Pteridine, 6-methyl-3,4-dihydro-structure, 3, 279... 

Isotripiperideine and a-tripiperideine structures differ from each other in a new C—C bond formed in is otripiperideine by an aldol reaction (296, 297). In aqueous media at pH 2-13, two molecules of -piperideine yield tetrahydroanabasine (297). 

The ratio of products 15 and 16 is dependent on the structures, base, and the solvent. The kinetics of the reaction is likewise dependant on the structures and conditions of the reaction. Thus addition or cyclization can be the rate-determining step. In a particularly noteworthy study by Zimmerman and Ahramjian, it was reported that when both diastereomers of 20 were treated individually with potassium r-butoxide only as-epoxy propionate 21 was isolated. It is postulated that the cyclization is the rate-limiting step. Thus, for these substrates, the retro-aldolization/aldolization step reversible. ... 

The Pictet-Spengler condensation has been of vital importance in the synthesis of numerous P-carboline and isoquinoline compounds in addition to its use in the formation of alkaloid natural products of complex structure. A tandem retro-aldol and Pictet-Spengler sequence was utilized in a concise and enantioselective synthesis of 18-pseudoyohimbone. Amine 49 cyclized under acidic conditions to give the condensation product 50 in good yield. Deprotection of the ketone produced the indole alkaloid 51. 

The dihydropyrones are not produced directly in the initial BINOL-titanium(IV)-cat-alyzed reaction. The major product at this stage is the Mukaiyama aldol product which is subsequently cyclized by treatment with TFA [19fj. The formal cycloaddition product 3d (97% ee) obtained from a-(benzyloxy)acetaldehyde is an important intermediate for compactin and mevinolin. Scheme 4.13 outlines how the structural subunit 13 is available in three steps via this cycloaddition approach [19 fj. 

Hie metliod involves a tegioselective, /vons-diasteteoselective, and eaantioselective tliree-component coupling, as shown in Sdieme 7.26. In tliis case, tlie zinc eaolate tesulling from tlie 1,4-addilion is trapped in a palladiuni-calalyzed allyla-tion [64] to afford /voiis-2,3-disubstituted cyclobexanone 96. Subsequent palladiuni-calalyzed Wacket oxidation [82] yields tlie metliylketone 97, wbidi in tlie presence of/-BuOK undergoes an aldol cyclization. This catalytic sequence provides tlie 5,6-i98) and 5,7- i99) annulated structures witli ees of 9696. 

The enantiomers are obtained as a racemic mixture if no asymmetric induction becomes effective. The ratio of diastereomers depends on structural features of the reactants as well as the reaction conditions as outlined in the following. By using properly substituted preformed enolates, the diastereoselectivity of the aldol reaction can be controlled. Such enolates can show E-ot Z-configuration at the carbon-carbon double bond. With Z-enolates 9, the syn products are formed preferentially, while fi-enolates 12 lead mainly to anti products. This stereochemical outcome can be rationalized to arise from the more favored transition state 10 and 13 respectively ... 

A syn-selective asymmetiic nih o-aldol reaction has been reported for structurally simple aldehydes using a new catalyst generated from 6,6-bis[(tiiethylsilyl)ethynyl]BINOL (g in Scheme 3.18). The syn selectivity in the nitro-aldol reaction can be explained by steric hindrance in the bicyclic transition state as can be seen in Newman projection. In the favored h ansition state, the catalyst acts as a Lewis acid and as a Lewis base at different sites. In conbast, the nonchelation-controlled transition state affords anti product with lower ee. This stereoselective nitro-aldol reaction has been applied to simple synthesis of t/ireo-dihydrosphingosine by the reduction of the nitro-aldol product with H2 and Pd-C (Eq. 3.79). 

Thomson -JOnV Click Organic Interactive to learn to draw the structures of products from aldol-type condensation reactions. 

The exact position of the aldol equilibrium depends both on reaction conditions and on substrate structure. The equilibrium generally favors condensation product in the case of aldehydes with no a substituent (RCH2CHO) but favors reactant for disubstituted aldehydes (R2CHCHO) and for most ketones. Steric Factors are probably responsible for these trends, since increased substitution near the reaction site increases steric congestion in the aldol product. 

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