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Masamune Macrolactonization

In the total synthesis of the macrolide antibiotic methymycin 49), Masamune and coworkers [28] developed a new macrolactonization method which makes use of the electrophilicity of Hg(II) toward bivalent sulfur. It involves the S -f-butyl thiolester 44 of the hydroxy acid 41 and employs mercuric trifluoroacetate as an activating agent. The required S -r-butyl thiolester 44 can be prepared in high... [Pg.116]

Masamune et al. [42] developed the macrolactonization of to-hydroxy r-butyl thioester with Hg(OCOCp3)2 in MeCN at room temperature, and this method accomplished the first total synthesis of methynolide [1]. They further developed an alternative method using a phosphoric acid mixed anhydride, which was apphed to the synthesis of narbonolide [43] and tylonolide [44]. [Pg.192]

The intramolecular HWE reaction in the presence of DBU was employed for the synthesis of (+)-rhizoxin D (71) by Jiang et al. [17]. Reaction of the aldehyde 69 with DBU-LiCl (Masamune-Roush conditions) [ 18] in acetonitrile at room temperature under high dilution conditions constructed the C2—C3 bond to form the macrolactone 70 (Scheme 7.14). Further elongation of the C20—C21 bond achieved the total synthesis of 71. [Pg.221]

The first total syntheses of racemic zearalenone (rac-479) were reported in the 1960s by the Merck and Syntex research groups (364, 365). In their multistep synthesis routes of the seco acid, the double bond was introduced by a Wittig reaction, but the required ( )-configured double bond was not formed selectively and the yields of the following lactonization were very low. The yields of macrolactonization were improved remarkably by Corey (360) and Masamune (361) using new activation methods for carboxylic acids (366). In aU the syntheses of zearalenone, the macrolide was formed by lactonization, but numerous possibilities are evident for the cyclization step. Figure 9.4 illustrates some different approaches to the synthesis of zearalenone (367). [Pg.94]

Masamune used the S-tert-butyl ester as an intermediate in the total synthesis of 6-deoxyerythronolide B (17), and activation of the thioester by a heavy metal efficiently promoted cyclization to form the desired polyoxygenated macrolactone (Scheme 5.3) [25]. [Pg.197]

Masamune et al. [53] and Corey et al. [54] explored phosphorus-based reagents such as diphenylchlorophosphate 38 [55], Palomo s reagent 39 [56], PyBroP 40 [57], and PyBOP 41 [58] in macrolactonization (Figure 6.14). Peptide coup-Hng agents of carbodiimide class, such as 42a,b, also were explored by Boden and Keck [59] as activators for macrolactonization with DMAP as a base (Figure 6.14). [Pg.238]


See other pages where Masamune Macrolactonization is mentioned: [Pg.402]    [Pg.402]    [Pg.130]    [Pg.181]    [Pg.471]    [Pg.20]    [Pg.94]    [Pg.279]   
See also in sourсe #XX -- [ Pg.402 ]

See also in sourсe #XX -- [ Pg.402 ]




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Macrolactonization

Macrolactonizations

Masamune

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