New PDF release: Activation by Charcoal

By Bancroft W. D.

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As can be seen in Table 6, even aliphatic aldehydes can be used to provide good yield and excellent enan- 50 M. r. 30 39 37 92 92 98 98 95 75 90 90 89 36 Scheme 6 Vinylogous aldol reactions with different catalyst loading tiomeric excess (Table 6, entry 4). The authors observed that free alcohols isolated in small quantities showed higher ee values than those derived from acidic deprotection, in which racemization in the deprotection step was accounted for. Another synthetically important feature of this reaction is the fact that the aldol reaction essentially takes place at room temperature.

Ata A, Kerr RG, Moya CE, Jacobs RS (2003) Tetrahedron 59:4215 5. Rodríguez AD, Ramírez C (2001) J Nat Prod 64:100 6. Rodríguez AD, Shi Y-P (2000) Tetrahedron 56:9015 7. Harvis CA, Burch MT, Fenical W (1988) Tetrahedron Lett 29:4361 8. Ata A, Kerr RG (2000) Tetrahedron Lett 41:5821 9. Rodríguez AD, Ramírez C, Rodríguez II, González E (1999) Org Lett 1:527; for stereochemical reassignment see Refs. [5] and [28] 40 T. J. Heckrodt · J. Mulzer 10. 11. 12. 13. Look SA, Fenical W, Matsumoto GK, Clardy J (1986) J Org Chem 51:5145 Roussis V, Wu Z, Fenical W (1990) J Org Chem 55:4916 Lazerwith SE, Johnson TW, Corey EJ (2000) Org Lett 2:2389 Tanaka J-I, Ogawa N, Liang J, Higa T, Gravalos DG (1993) Tetrahedron 49:811; for structural revision see Ref.

Abstract The synthesis of complex natural products still remains as the bottleneck for the biological evaluation of such compounds. In contrast to the biosyntheses, vinylogous aldol reactions can incorporate more than one acetate or propionate building block into the growing polyketide chain. To facilitate such reactions either enolate activation or aldehyde activation is required. For both variations, selective protocols have been put forward and were shown to be efficient substitutes compared to standard aldol reactions.

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Activation by Charcoal by Bancroft W. D.

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