Alkyl S -lactates

Alkylene bromide, 20, 24 Alkylene thioureas, 26, 35 Alkylidenecyanoacetic esters, 25, 48 Alkyl lactate, 26, 6 Alkyl phenyl selenides, 24, 91 S-Alkylthiuronium halides, 22, 60 d/-ALLOTHREONINE, 20, 104 Alloxan, 23, 3 

In the past Lewis acid-catalyzed [4+2] cycloaddition reactions of chiral alkyl acrylates have been systematically studied. Chiral auxiliaries derived from camphor, menthol and amino acids or from carbohydrates have been developed. Stereochemical and theoretical aspects of these chiral inductors have been intensively reviewed (see. Chapter 6). Asymmetric Diels-Alder reactions of chiral acrylamides derived from Ca-symmetrical secondary amines lead selectively to the cycloadducts in the presence of Lewis acids such as AICI3. In reactions of chiral auxiliaries derived from (iS)-proline and (iS)-prolinol excellent endo/exo selectivities and diastereoselectivities were obtained in the presence of catalytic amounts of Et2AlCl or TiCL. Cycloadducts of chiral crotonoyl derivatives derived from oxazolidinones 62, sultam 63 or for example (S)-lactate IS were obtained with high selectivities in the presence of Lewis acids such as Et2AICl. 

Hydrogenation of alkyl pyruvates to their corresponding lactates have received considerable attention both from a theoretical and experimental standpoint. Some example results are shown in Table 9.3. Enantioselectivity in these systems is measured in terms of enantiomeric excess (ee) which is defined as ([R] - [S])/([R] + [S]). 

Protection of ethyl L-lactate with a MEM group is easily accomplished by alkylation with (2-methoxyethoxy)methyl chloride in the presence of Hunig s base (2- 372) [100,116,117]. 

Asymmetric reduction of a-keto esters.3 Alkyl pyruvates are rapidly reduced by this borane to alkyl (S)-lactates (equation I). The extent of asymmetric induction depends to some extent on the temperature and the size of the ester group. Quantitative optical 

L-( + )-Lactic acid (1), the naturally occurring form, is commercially available from a large number of suppliers, and is inexpensive. At this writing, the price of 1 kg is less than 60. Although 1 may be esterified with an alkyl iodide in the presence of CsF [1], carrying out this process is unnecessary since many lactic acid esters are commercially available, and some are even less expensive then the parent acid. For example, 500 g of ethyl ( S)-( — )-lactate (2) can be purchased for less than 14. 

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