Partial Reduction of Pyridinium Salts as a Versatile Route to Dihydropyridones.

Abstract

Pyridine derivatives R 0380Partial Reduction of Pyridinium Salts as a Versatile Route to Dihydropyridones.-A concise route to the title compounds includes the reduction of the pyridinium salts under ammonium-free conditions and the subsequent reaction with a variety of electrophiles as the key steps. The chemistry of the products is investigated showing that every position in the ring can be derivatized by standard synthetic methods. -(DONOHOE*, T. J.; JOHNSON, D. J.; MACE, L. H.; BAMFORD, M. J.; ICHIHARA, O.; Org. Lett. 7 (2005) 3, 435-437; Dep. Chem., Univ. Oxford, Oxford OX1 3QR, UK; Eng.) -Steudel 24-131

Formation of N-Boc pyrrole 2,5-methyl diester, a key intermediate in the Donohoe synthesis of 1-epiaustraline and hyacinthacine A1.

“…The Birch (Li/NH 3 ) and ammonia-free (Li/di-tert-butyl biphenyl [DBB]) 1 partial reductions, using the conditions developed by Donohoe, are applicable to a wide range of heteroaromatic compounds with a variety of substitution patterns, resulting in formation of the respective dihydro compounds in typically good to excellent yields. [2][3][4][5][6][7][8] The reduction of the N-Boc pyrrole whose formation is described herein, 9 (Figure 1) has recently been published by Donohoe et al as a key step in the routes to the biologically active natural products 1epiaustraline and hyacinthacine A 1 . 10,11 CRITICAL The methyl chloroformate should be passed through a short plug of magnesium sulfate and potassium carbonate prior to use in order to remove any residual water or acid present.…”

Formation of N-Boc pyrrole 2-ethyl ester, a key intermediate in the Donohoe synthesis of omuralide.

“…The Birch (Li/NH 3 ) and ammonia-free (Li/di-tert-butyl biphenyl [DBB]) 1 partial reductions, using the conditions developed by Donohoe, are applicable to a wide range of heteroaromatic compounds with a variety of substitution patterns, resulting in formation of the respective dihydro compounds in typically good to excellent yields. [2][3][4][5][6][7][8] The reduction of the N-Boc pyrrole whose formation is described herein, 9 (Figure 1) has recently been published by Donohoe et al as a key step in the route to the biologically active natural product omuralide. 9,10…”