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Strigol synthetic studies the first synthetic approach that allows control of C-2′ configuration

✍ Scribed by Katja Frischmuth; Andreas Marx; Tanja Petrowitsch; Ulrich Wagner; Klaus Koerner; Silke Zimmermann; Heike Meuer; William S. Sheldrick; Peter Welzel

Publisher
Elsevier Science
Year
1994
Tongue
French
Weight
355 KB
Volume
35
Category
Article
ISSN
0040-4039

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✦ Synopsis

A phenylthio group has been used to control stereoselectivt bond formation at C-2'. Germination of seeds of root parasitic flowering plants of tht genera Striga, Alec&a (Scrophulariaceae), and Oroti (Orobanchaceae) is stimulated by substances from their host plants Prominent examples are strigo! and sorgolactone.' Scheme 1 Very specific interactions between the stimulant and the biding site(s) at the seed seem to exist. For orobonche cfenata seeds it has been found that the absolute configuration at C-2' is of major importance as fkr as seed germbwtion potency is concerned. ' Non-race&c samples of strigol, its stereoisomers, and of structural analogues have been obtained both by resolution2 s3 p4 *5 and by asymmetric synthesk6 v7 However, fbr one stereochemical problem no solution has previously been found, namely control of the contiguration at C-2'. In all cases reported so far, a synthetic intermediate of type 1 was converted into a hydroqnethykne derivative 3 which was in turn coupled with racemic, configurationally unstable bromo lactone 4 to give a 1: l-mixture of 2'-epimers such as 5 and 6 3.4.7,s .9 .I0 It is the purpose of this publication to discuss preliminary results which indicate that this di&uity can be mastered. The stereohomogeneous sbigol analogue GR 28 (5) and its 2'-epimer 6 have been obkned stereoselectively. The precursors and &erence samples were prepared starting from rat-2 which was qcliztd with cat. Pd(OAcbl' to provide m-l.12 Resolution of mc-1 was achieved by ctllulose triacttatc chromatography. 1" was then converted to 513 and 6" via 3. Sii, ent-5 and ent-6 were obtained from ent-1. The relative configuration at C-2' in 5 and 6 rests on X-my analysi~.'~ The absolute configuration was

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