Andersen procedure

The Andersen procedure for the synthesis of ENANTIOMERICALLY ENRICHED, CHIRAL SULFOXIDES 41... 

The Andersen Procedure for the Synthesis of Enantiomerically Enriched, Chiral Sulfoxides... 

Johnson was able to overcome the synthetic limitations of the Andersen procedure by inducing the displacement of aryl groups from diaryl or alkyl aryl sulfoxides with either alkyllithium or alkyl sodium reagents as a general approach to optically active, unsymmetrical dialkyl sulfoxides (Scheme 2.4, Table 2.1) [13]. 

Another drawback of the classical Andersen procedure is that it allows for isolation of diastereoisomerically pure (5)-(-)-menthyl p-toluene sulhnate in a poor 30% yield. An early improvement pioneered by Hebrandson employed the known racemization of sulfoxides by HCl in an epimerization/equilibration technique to increase the yield of (5)-(-)-menthyl p-toluene sulhnate to 90% from the initial (R) and (5) diastereoisomeric mixture [14]. This adaptation has been described in detail by Solladie and the proposed epimerization/equilibration is... 

Table 2.3 Use of organolithium cuprate reagents as alternatives to Grignard reagents in the Andersen procedure...

Mikolajczyk observed much increased yields, without loss of optical purity, in the Andersen procedure by simply ehanging the solvent from diethyl ether to benzene (Scheme 2.10, Table 2.4) [18]. 

More reeently, Whitesell has recently reported an improved method for the preparation of enantiomerically pure sulfinate esters (Scheme 2.11) [19]. As previously described, the (5)-(-)-menthyl p-toluene sulfinate diastereoisomer only is readily available in a pure, crystalline form using the Andersen procedure. Whitesell discovered that reaction of the ehiral auxiliary trans-2-phenylcyclohexanol (8) with an excess of alkyl or arene sulfinyl chloride afforded the appropriate sulfinate esters (9) and (10) in good yield and with better selectivities (up to 10 1) than those observed with (lf ,25,5f )-(-)-menthol ( 2 1). These diastereoisomers can be readily separated (R p-Tol (9a) = 62% yield, 98% de) by either crystallization or by chromatography, in contrast to the Andersen procedure. 

This reaction is more stereoselective than the corresponding synthesis of menthyl sulfinate diastereoisomers in the Andersen procedure, allowing for easier fractional crystallization. Optically active (/ )-(+)-methyl phenyl sulfoxide (13) is obtained on reaction of (lf ,2S)-(12) with methyllithium (Scheme 2.14). 

The A -sulfinyloxazolidinones have also been demonstrated to be highly efficient reagents for the synthesis of dialkyl sulfoxides in high yields and with excellent enantioselectivities as discussed, this class of sulfoxide has proved to be inaccessible through the Andersen procedure. Examples are highlighted in Scheme 2.17 and Table 2.6 for A-sulfinyloxazolidinone (16). 

In conclusion, Snyder and Benson s approach allows the synthesis of enantiomerically pure dialkyl and alkyl aryl sulfoxides in good yields and with excellent enantioselectivities. Both enantiomers are accessible by reversing the order of organometallic displacement or by employing the (15,2J )-(+)-ephedrine enantiomer. The only limitations are observed in the synthesis of t-butyl phenyl and aryl phenyl sulfoxides. However aryl phenyl sulfoxides are accessible by the Andersen procedure, and t-butyl phenyl sulfoxides by an approach to chiral sulfoxides developed by Kagan, described below. 

The essence of Monte-Carlo models is to calculate the path of an ion as it penetrates a crystal. Early versions of these models used the binary collision approximation, i.e., they only treated collisions with one atom at a time. Careful estimates have shown that this is an accurate procedure for collisions with a single row of atoms (Andersen and Feldman, 1970). However, when the rows are assembled into a crystal the combined potentials of many neighboring atomic rows affect ion trajectories near the center of a channel. For this reason, the more sophisticated models used currently (Barrett, 1971, 1990 Smulders and Boerma, 1987) handle collisions with far-away atoms using the continuum string approximation,... 

The procedure most commonly used for the stereospecific preparation of optically active sulfoximides involves the reaction of optically active sulfoxides with arylsulfonyl azides in the presence of copper (98,118,131,178,179). This reaction occurs with retention of configuration at sulfur and with high stereospecificity. The stereospecific sulfoxide-sulfoximide conversion is a key reaction in the stereospecific sulfoxide-sulfimide-sulfoxiraide set of interconversions carried out by Cram and co-workers (98) and shown in Scheme 9. A similar cycle of interconversions studied independently by Andersen and co-workers (179) was used to determine the stereochemical course of the sulfoxide-sulfoximide transformation (see Scheme 10). 

We will consider in some detail only one of these procedures—that of Andersen, Beyer, and W atson, as modified by Yoneda [4]—to Ulustrate the type of approach used in these approximation methods. 

The procedure followed in the use of the tables of Andersen et al. [1], and Yoneda [4] is illustrated below for the estimation of standard entropies. These tables also include columns of base structure and group contributions for estimating fHm,298.i5K> thc Standard enthalpy of formation of a compound, as well as columns for a, b, and c, the constants in the heat capacity equations that are quadratic in the temperature. Thus it is possible to estimate AfGm gg.isK by appropriate summations of group contributions to Af7/ 298.i5K and to 5m,298.i5K- Then, if information is required at some other temperature, the constants of the heat capacity equations can be inserted into the appropriate equations for AG, as a function of temperature and AGm can be evaluated at any desired temperature (see Equation 7.68 and the relation between AG and In K). 

These examples illustrate the procedure used in the Andersen-Beyer-Watson-Yoneda method. The hrst example shows moderate agreement the second shows poor agreement. Generally, it is preferable to consider the group substitutions in the same order as has been used in the presentation of the tables. The best agreement with experimental values, when they are known, has been obtained by using the minimum number of substitutions necessary to construct the molecule. For cases in which several alternative routes with the minimum number of substitutions are possible, the average of the different results should be used. 

The initial procedures involved in expression of the Rhodnius nitrophorins in Escherichia coli were worked out for NPl by Drs. Donald E. Champagne and John F. Andersen at the University of Arizona during the spring and summer of 1996, and the purification protocols were... 

Both enantiomers of methyl p-tolyl sulfoxide are available from the above procedure by selection of the appropriate diethyl tartrate. This procedure describes the preparation of (S)-(-)-methyl p-tolyl sulfoxide which is not easy to prepare by the Andersen method " using (+)-raenthol. 

Andersen P, Petersen NC (1993) A Procedure for Ranking Efficient Units in Data Envelopment Analysis. Management Science 39 1261-1264... 

The reaction of 2 equiv of /V,/V-dimethylhydrazone 97, obtained by standard procedure, with 2 equiv of n-BuLi gave the corresponding a-lithioderivative, which on reaction with methanesulfinates 87 (R = Me) and 88 (R = Me) yielded o.p. sulfoxides 985 and 98R, respectively, in high yield. The configurational assignment of the a-sulfinyl hydrazone obtained was made assuming that the condensation step occurs with complete inversion of configuration at the sulfinyl sulfur, as is the case for many Andersen-type reactions. 

A method that makes available aromatic and aliphatic aldehyde derived sulfin-imines 47, for the first time, was recently introduced by Davis and co-workers.23,36 This one-pot procedure entails treatment of the Andersen reagent 40 with LiHMDS to generate 44 which subsequently reacts with the lithium methoxide by-product to produce silyl sulfinamide anion 46. Reaction of 46 with the aldehyde in a Peterson-type olefination reaction affords the sulfinimine 47 in >96% ee. This method was highly effective for the preparation of arylidene sulfmamides 47 (R = aryl) which were usually obtained in 60-76% yield although the alkyl counterparts... 

The measurement of standard reference materials (SRMs) provides the best method for ensuring that an analytical procedure is producing accurate results in realistic matrices. Many SRMs are available (Govindaraju, 1994 Rasmussen and Andersen, 2002). The most widely used are those supplied by National Institute of Standards and Technology (NIST). Arsenic and selenium concentrations have been certified in a range of natural waters, sediments, and soils (Tables 4 and 5). The SLRS range of certified standards from the National Research Council of Canada also includes several river waters with much lower arsenic concentrations than the NIST standards ( 0.2-l pgL ). Certified standards for As(III)/As(V) and Se(lV)/Se(VI) speciation are available commercially (e.g., SPEX Certiprep speciation standards). 

Many organosulfur compounds can be resolved into optically active forms (enantiomers) owing to the presence of a chiral (asymmetric) sulfur atom 5 important examples include sulfoxides and sulfonium salts. Chiral sulfoxides containing amino or carboxylic acid groups have been resolved by formation of the diastereoisomeric salts with d-camphor-10-sulfonic acid or d-brucine. The salts can then be separated by fractional crystallisation and the free optically isomeric sulfoxides liberated by acid hydrolysis. However, a more convenient synthetic procedure for the preparation of chiral sulfoxides of high optical purity is Andersen s method (see p. 30). 

Bytzer P, Stokholm M, Andersen I, Klitgaard NA, de Muckadell OBS. Prevalence of surreptitious laxative abuse in patients with diarrhoea of uncertain origin. A cost benefit analysis of a screening procedure. Gut 1989 30 1379-84. 

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