Abstract
A new and direct approach to the construction of the core framework of the herbicidal natural products cornexistin and hydroxycornexistin has been developed. Formation of the nine-membered carbocycle found in the natural products has been accomplished by an intramolecular Nozaki-Hiyama-Kishi reaction between a vinylic iodide and an aldehyde. Good yields of carbocyclic products were obtained from the reaction, but diastereomeric mixtures of allylic alcohols were produced. The cyclisation reaction was successful irrespective of the relative configuration of the stereogenic centres in the cyclisation precursor.
Highlights
The selective and potent herbicidal activity of the cornexistins combined with their apparently novel mode of action and non-persistence in the environment means that these natural products have significant potential as lead compounds in the search for novel, biorational post-emergence weed control agents that can be used in arable crop production
The cornexistins have significant potential as novel lead compounds in the search for new herbicides, they have been the subject of few synthetic studies and very little has been published concerning their total synthesis
This approach did not culminate in the total synthesis of either natural product. Our interest in both cornexistin and hydroxycornexistin as targets for total synthesis was aroused by the combination of the synthetic challenges presented by the natural products and their potent herbicidal activities. Both compounds possess a relatively rare nine-membered carbocycle fused to a highly reactive maleic anhydride unit, a combination of structural features that poses a formidable test to conventional methods of ring construction
Summary
Isolation and Herbicial Activities of the Cornexistins Cornexistin and hydroxycornexistin are structurally unique members of the nonadride family of naCtuorranlexpirsotidnuacntsd(hFiygdurroexy1c)o[r1n–e5x].istCinoranreexsitsrtuinctuwraasllyfirusntiiqsuoelamteedmfbroemrs oafctuhletunroenoafdrthideeffuanmgiulys Pofaencialtoumryacleps rvoadruiocttisi (BFaiginuireer 1()st[r1a–in5].SCAoNrnKex2i1st0i8n6)wbays frierssteaisrochlaetresd aftroSmanakycoultCuore. Ofinth1e98fu7nagnuds Phyaedcrilooxmyyccoersnevxairsiotitnii wBaasiniiseorla(tsetdraifnromSAtNheK sa2m10e86s)trabiyn roefsetharechfuenrsguast bSyanwkoyrokeCrso.atinDo1w98E7laanncdo heiygdhrtoyxeyacrosrnlaetxeirs.tBinowthacsoimsoplaotuedndfsrohmavteheatstarmacetesdtrtahine ionftethreesftuonfgtuhse baygrwocohrkemeriscaatl iDnodwusEtlraynbcoeceaiughset yoef atrhselaptoetre. NBtoathndcosmelpeoctuivnedshherabvieciadtatrlaacctetidvitthieesinthteeryesptoosfsethsse aagnrdocbheecmauiscealtihnedyuastrreypbreocnaeustoe oraf pthide pdoegternatdaatniodn osenleecxtpivoesuhreertboilciigdhatl oarcwtivhietnietsretahteeyd wpiotshsaescsidaonrdbabseec[a6u].seThtehceoyrnaerxeisptirnosnaeretuonuraspuiadl dmeegmrabdearstioonf tohne enxopnoasdurrideetofalmigihlyt oorf wnahteunratlrepartoedduwctisthbeaccaiudsoerthbeaysep[o6s]s. ETshseacsoirnngeleximstainlesicaraenuhnyudsruidael muneimt ebmerbseodfdtehde innotnhaedirrisdterufactmurileysowf hnearteuarsalmporsotdoufctthsebeocthauersentohneaydpriodsessespsoassseinssgtlewmo a[7le].ic anhydride unit embedded in their structures whereas most of the other nonadrides possess two [7]. The selective and potent herbicidal activity of the cornexistins combined with their apparently novel mode of action and non-persistence in the environment means that these natural products have significant potential as lead compounds in the search for novel, biorational post-emergence weed control agents that can be used in arable crop production
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