Of configuration in reactions

Alkylation of dihydropyranylacetates. The Pd(0)-catalyzed alkylation of allylic acetates by stabilized carbanions originally reported by Trost and Verhoeven (8,475 9, 451 -457)4 has been extended to alkylation of dihydropyranyl acetates as a route to natural C-glycopyranosides.5 Again the displacement is regioselective and results in net retention of configuration in reactions with most carbanions. However, alkylation with phenylzinc chloride or vinylzinc chloride occurs with inversion. 

Nucleo diiiic Substitution.—Further studies with unhindered secondary hydroxy-steroids confirm earlier reports of almost total inversion of configuration in reactions with PCls. However, thionyl chloride is less efficient than is generally believed in giving chloro-compounds with retention of configuration (SnI reaction). Thus 5a-cholestan-3a- and -3/5-ol with thionyl chloride each gave mixtures of... 

On the other hand, the fluorine-induced addition of the diastereomeric silyl-subsliluted sulfides 36 A and 36B to benzaldehyde proceeds without loss of stereochemical information and with retention of configuration32. Since, however, the anionic reagent 35A/35B is known to be configurationally labile, the observed retention of configuration in the fluorine-induced desi-lylative hydroxy alkylation lends experimental evidence to the notion that these reactions proceed via hypervalent silicon species rather than anionic reagents. 

Cycloaddition reactions can occur with retention of configuration in the pseudoexcitation band (Sect 1.1) whereas [2jt H-2jtJ reactions are symmetry-forbidden in the delocalization band. Experimental evidence is available for the stereospecific [2-1-2] cycloaddition reactions between A and olefins with retention of configuration (Scheme 14) [82]. A perepoxide intermediate was reported to be trapped in the epoxide form [83] in the reaction of adamantylideneadamantane with singlet oxygen affording dioxetane derivatives [84]. 

Cycloaddition reactions with the Si(lOO) surface have been investigated for the purpose of designing microelectronics, nonlinear optical materials, sensors, and biologically active surfaces. The features of the [2+2] cycloadditions characteristic of the reactions in the pseudoexcitation band [133] predicts that [2+2] cycloadditions of electron-donating alkenes with Si(100)-2 x 1 surface could proceed with retention of configurations, in agreement with the observation [134]. Such stereospecific functionalizations of surfaces are of potential use for specific applications. 

Benschop and his co-workershave shown that ethyl phenylphosphinate (140) may be converted into ethyl alkylphenylphosphonites (141) by a variety of routes based on the Arbusov reaction, with retention of configuration in each case. 

There are also some examples of retention of configuration in nucleophilic displacement reactions where the common feature is an atom or group—close to the carbon undergoing attack—which has an electron... 

This reaction has been used a good deal in the study of carbanions, to detect their formation by converting them into stable, identifiable products. Thus substantial retention of configuration in an alkenyl carbanion (37) has been demonstrated, in the reaction of (38) with... 

In the carbohydrate chemistry arena, the Tsuji-Trost reaction has been applied to construct N-glycosidic bonds [53]. In the presence of Pd2(dba>3, the reaction of 2,3-unsaturated hexopyranoside 68 and imidazole afforded N-glycopyranoside 69 regiospecifically at the anomeric center with retention of configuration. In terms of the stereochemistry, the oxidative addition of allylic substrate 68 to Pd(0) formed the jc-allyl complex with inversion of configuration, then nucleophilic attack by imidazole proceeded with another inversion of the configuration. Therefore, the overall stereochemical outcome is retention of configuration. 

R R2CHOH -> RlR2CHCl. This transformation can be effected with retention of configuration in two steps conversion to the methyl xanthate followed by reaction with sulfuryl chloride (equation I). 

Sukenik and Bergman, 1976). This material gives 2-octanol with 100% inversion of configuration in non-micellar and CTAB-micellar systems, but in the presence of the SDS micelle the reaction is strongly inhibited and there is a significant change (56% inversion) in stereochemistry. 

An interesting comparison has been made between the behaviour of (78)—(80) in their reaction with Cl2 and SOaCla.61 Compounds (78) and (79) react at -70 °C via phosphonium-like intermediates, with retention of configuration in the former case the product is the phosphonic chloride (81) whereas (79) yields the cyclic oxophos-phoranesulphenyl chloride (82). On the other hand, the benzodioxaphospholan (80)... 

The procedure described here provides a stereospecific synthesis of (E)- and (Z)-fluoroalkenes from the corresponding (E)- and (Z)-fluorovinyl sulfones. Fluorovinyl sulfones obtained from ketones are, in most cases, readily separable into (E) and (Z) isomers either by crystallization or by chromatography.4 In the example described, only the (E)-fluorovinyl sulfone 1 is formed (which is converted into the (Z)-fluoroalkene 3 with complete retention of configuration). The reaction sequence has been used for the stereospecific synthesis of fluoroalkene nucleosides5 as well as for... 

Historically, the thermal transesterification of (-)-ethyl p-toluene-sulfinate 224 with n-butanol affording (+)-n-butyl p-toluenesulfinate 225 described by Phillips in 1925 (100) is the first nucleophilic substitution reaction at chiral sulfur involving a Walden-type inversion. The evidence for inversion of configuration in this reaction was based on the assumption that both (-)-esters 224 and 225 obtained from the kinetic resolution have the same configuration. 

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