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11
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84918463604
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T. Nakata, M. Fukui, and T. Oishi, to be published.
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12
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84918463603
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Recently we reported highly stereoselective synthesis of macrolide aglycons such as methynolide, pikronolide, and tylonolide.
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16
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84918463602
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3 was already converted to 1 and 2.
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17
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84918463601
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Unless otherwise noted, the numberings are based on that of 3.
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18
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37049092702
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Chiral synthesis of polyketide-derived natural products. Part 4. Synthesis of a left-hand segment with six consecutive chiral centres of dihydroerythronolide A for the total synthesis of erythromycin A from D-glucose
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and alternative synthesis of 6 from propionaldehyde will be reported soon.
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(1985)
Journal of the Chemical Society, Perkin Transactions 1
, pp. 7
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Oikawa1
Nishi2
Yonemitsu3
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22
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84918463600
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4 in ether, etc.) gave only poor results.
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27
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84918463599
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Protection of 9,11-diol, not of 11,12-diol, as a cyclic acetal is extremely important for the macrolactonization.
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30
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84918463598
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4 is a 1 : 1 stereoisomeric mixture with regard to the SO position.
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31
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37049093660
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Chiral synthesis of polyketide-derived natural products. Part 5. Synthesis of a chiral segment corresponding to the C-1?C-5 unit of erythromycin A from D-glucose
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and an alternative synthesis of 13 from methallyl alcohol via the Sharpless asymmetric epoxidation will be reported soon.
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(1985)
Journal of the Chemical Society, Perkin Transactions 1
, pp. 19
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Oikawa1
Nishi2
Yonemitsu3
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33
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84918463597
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Corey's method (NBS, 2,6-lutidine, 80% MeCN, rt) also gave 5 in 71% yield.
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35
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84918463596
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Most of excess 4 was recovered (86%). Coupling between 4 and the 6-methylketone derived from 5 gave only poor results in <20% yield.
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36
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84918463595
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2, in THF, no reaction occurred.
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40
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84918463594
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In this macrolactonization, concentration of DMAP was very important. Yields of 19 in various concentrations of DMAP are as follws [final mM of DMAP (% yield of 19)]: 25 mM (27%); 9.5 mM (14%); 6 mM (13%); 3 mM (0%).
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41
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84918463593
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As pointed out by Stork, an axial methyl group of 9,11-acetonide protection hindered this lactonizition. Actually we, could not obtain 19 by the modified Corey method, and also 20 gave only a trace of lactonization product, which was, however, obtained in 63% yield by highly reactive Yamaguchi's method at high concentration of DMAP.
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42
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84918463592
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3, 18, 19, and a 6-O-MM derivative of 21 were identical with the respective authentic samples derived from natural erythromycin A in terms of IR, NMR, and MS spectra.
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