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Tetrahedron Letters
Volumn 19, Issue 19, 1978, Pages 1685-1688
Acyclic stereoselection. III. Synthesis of threo-3-hydroxy-2-methylcarboxylic acids
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EID: 0001529746     PISSN: 00404039     EISSN: None     Source Type: Journal    
DOI: 10.1016/S0040-4039(01)94640-4     Document Type: Article
Times cited : (131)
References (9)
  • 3
    • 84918985168 scopus 로고    scopus 로고
    • Hydroxy acid 2 is most easily obtained by condensing the enolate of methyl propionate with benzaldehyde. The resulting mixture of hydroxy esters (erythro/threo ≈ 1.5:1) is then hydrolyzed with KOH in methanol, whereupon the less soluble threo salt crystallizes. This salt is collected, neutralized, and recrystallized to afford nearly pure 2.
  • 5
    • 84918985166 scopus 로고    scopus 로고
    • Although only one enantiomer is depicted for each compound, all are racemates.
  • 7
    • 84918985164 scopus 로고    scopus 로고
    • Although no proof has been adduced, we believe that lactones 7 and 8 also have the configurations (RS,SR,RS) and (RS,RS,SR), on the basis of analogy. The “Cram's-rule selectivity in this case is nil (7/8 = 1:1).
  • 8
    • 84918985161 scopus 로고    scopus 로고
    • This argument presumes that the crotyl group retains the (E)-configuration throughout its transfer from chromium to carbon.
  • 9
    • 84918985158 scopus 로고    scopus 로고
    • After this manuscript was submitted, a paper appeared (J. Mulzer, J. Segner, and G. Bruntrup, Tetrahedron Letters, 4651, 1977)) which described the stereoselective synthesis of threo-3-hydroxycarboxylic acids by the condensation of carboxylic acid dianions with aldehydes. In some cases, excellent stereoselectivity was achieved under conditions of thermodynamic control (three days at 25° C). However, even under the best conditions, hydroxy acid 2 was produced in only 10% diastereomeric excess over the corresponding erythro isomer. Although the Hiyama method requires two steps rather than one, the excellent stereoselectivity observed in the formation of simple two-chiral center β-hydroxy acids such as 2 may render it the synthetic method of choice in these cases.

* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.