Relay synthesis

Iwao and Ishibashi [37] have utilized their methodology depicted in Scheme 13 for the preparation of ningalin B hexamethyl ether (91) with compound 71 functioning as the key precursor for this relay synthesis. This strategy appears to be very flexible for a wide variety of pyrrole natural products. 

Furstner s group has also developed [58] a very practical strategy (Scheme 24) for the relay synthesis of permethyl storniamide A (120) via an important diester (126), which was the precursor to the Boger diacid (118) presented in Scheme 23. 

In this method, Furstner converts N-BOC protected pyrrole to the 2,5-dibromo compound (122) with NBS and this is followed by metalation and carbomethoxylation with t-butyl lithium in THF and subsequent trapping of the metalated species with methyl chloroformate to yield a pyrrole diester (123). Bromination of this diester at positions 3 and 4 with bromine in water followed by Suzuki cross-coupling with 3,4,5-trimethoxyphenyl boronic acid yields the symmetrical tetrasubstituted pyrrole (125). Base-mediated N-alkylation of this pyrrole with 4-methoxyphenethyl bromide produces the key Boger diester (126) and thereby constitutes a relay synthesis of permethyl storniamide A (120). 

Iwao and Ishibashi [37 ] have also utilized their methodology presented in Scheme 13 to accomplish a relay synthesis of permethylstorniamide A and a brief representation of this route is given in Scheme 25. 

It should be noted that a relay synthesis of optically pure (-)-lycorine was also completed commencing with optically pure 66, which had been prepared from naturally occurring lycorine via the dihydrolycorine lactam 71 and the derived tosylate 72. The reduction of optically pure 66 resulted in the formation of a-dihydrocaranine (73) (108c). A straightforward synthesis of ( )-zephyranthine... 

Monosubstituted oxadiazoles (119 R = alkyl, aryl, hetaryl, styryl or C02Et) are formed in a relay synthesis from triazolylbenzamidines (118) on treatment with acid chlorides RCOC1 or anhydrides (RC0)20 (69JPR646). 

The diketo ester D was then converted to B. In the course of this work, both C and D could be provided by degradation of commercially available gibberellin A3. The relay synthesis of gibberellin A4 was completed in December 1967 just before Professor Yabuta s 80th birthday. Since the conversion of... 

The Leeds synthesis of vitamin D is also a relay synthesis. The relay compounds employed here are given in Scheme 12. 

The Woodward group conducted most of their remaining work with material prepared by degradation of cholesteryl acetate to tetracycle 20, which was also prepared from synthetic 1 as shown in (Steroids-4). A synthesis of a natural product from an intermediate prepared by degrading a natural product, prepared in turn by total synthesis, is known as a relay synthesis. This is a less common practice nowadays than in the early days of natural products synthesis, but it is not unheard of even today. We will see this practice again. 

Gupton, J.T, Krumpe, K.E., Burnham, B.S., Webb, T.M., Shuford, J.S., and Sikorski, (.A. (1999) The application of vinylogous imituum salt derivatives to a regiocontrolled and efficient relay synthesis of lukianol A and related marine natural products. Tetrahedron, 55, 14515-14522. 

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