Aldehydes erythro stereoisomers

Z)-2-Phenyl-2-butene. (Z)-2-pheny 1-2-butene is not as stable as its (E) isomer. When Co >(CO)8 is used, results are the same with the (E) stereoisomer. However, when rhodium is used, isomer selectivity changes (Table VIII). The main isomeric aldehyde is the erythro di-astereoisomer which represents 33.9% of the whole mixture. Aldehyde 27 is formed in nearly the same ratio (32.9% ) while 6.8% and 4.4% of aldehyde 26 and the threo diastereoisomer are formed. 

Ytterbium has the oxidation states 4-2 and -t-3. A stereochemical dichotomy exists in their enolate chemistry . Yb(II) enolates react with aldehydes to form the erythro-fi-hydroxyketones while Yb(III) enolates yield the threo stereoisomers. We fail to understand this by either thermodynamic or mechanistic reasoning. Analogous to corresponding reaction chemistry for samarium, preformed ytterbium benzophenone dimer, [Yb(Ph2CO) (HMPA)2]2, reacts " with sterically crowded phenols to form in low yield (5%) the enolate complex 22b by dearomatization of benzophenone. The major product (80%) is the... 

Erlenmeyer reaction The condensation reaction between an aromatic aldehyde and an A-acyl derivative of glycine, in the presence of acetic anhydride and sodium acetate, to give an azlactone. Erythro isomer The stereoisomer of CabxC.lby that is represented by the following diagram using... 

In the presence of (Pj-LLB (3.3 mol%), the treatment of AT-phthaloyl-L-phe-nylalanal 17 with nitromethane at -40 °C gave practically a single stereoisomer of (2P,3S/)-2-hydroxy-4-phenyl-3-phthaloylamino-l-nitrobutane 18 in 92% yield (>99 1 eryf/zro-selectivity) [25]. Interestingly, reaction of the (S)-aldehyde 17 with nitromethane, using the (S)-LLB complex as a catalyst, led to a reduced diastereo- and enantioselectivity (96% yield erythro/threo 74 26 90% ee(eryth-ro)). The conversion of the nitroaldol adduct 18 into 19 was achieved in one pot (80% yield). 

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