Overbred Intermediates NathanWilde Introduction January2013 Thisdogcanbarelysquint throughitsoverbredfacial foldstoseeanything. ThisgroupmeetingisbasedonasectioninHoffman'sbook Elements of Synthesis Planning called"'Overbred'Intermediates."Thissectiondefines "overbredintermediates"asintermediatesenroutetocyclicstructuresthat haveoneormoreexcessC-Cbonds,andthesesurplusbondswillneedto becleavedinsubsequentsteps.Thisgoesagainstlogicalretrosynthetic planning(insteadof findinggoodretrosynthetic disconnections youlookfor good "add bond" connections)andeventheparametersformeasuring againsttheidealsynthesis,butthegoalofthispresentationistolearnwhen suchintermediatesmightbestrategic. Notes: -IonlycareaboutmakingandcleavingC-Cbonds. -UsingDA/retro-DAtoprotectolefinsdoesn'tcountbecauseIsaysoand becauseitisnotinteresting. -NodegradationofcommerciallyavailableSM.Makethecomplexityand thendestroyit(theremaybeoneexceptioninthispresentation). -Thisisnotmeanttobeabashingparty.Therearelotsofbothgoodand badexampleshere.Wecanlearnfrombothtypes. -Bynaturewemustsomehowfragmentextraneousbondsinoverbred intermediates, so I consider this topic a subset of Shenvi's 2005 "Fragmentation Reactions in Synthesis" group meeting. longifolene O O addbond retroaldol O OH O OH HO 2 C H H O H Oppolzer. JACS 1978, 2583 addbond metal reduction H O h Coates. JACS 1985,3541 H O O OH H H O addbond MsCl, Grob H H OH OH HO West. JOC 1998, 2806 h A. Medium Rings HO 2 C
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OverbredIntermediates Introduction January2013 · NathanWilde OverbredIntermediates MediumRings January2013 Tan.Nat.Chem.Bio.2013,21 HO HO O O O TfO PhI(AcO) 2TfO 45% 91% HO2C HO
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This dog can barely squintthrough its overbred facialfolds to see anything.
This group meeting is based on a section in Hoffman's book Elements ofSynthesis Planning called "'Overbred' Intermediates." This section defines"overbred intermediates" as intermediates en route to cyclic structures thathave one or more excess C-C bonds, and these surplus bonds will need tobe cleaved in subsequent steps. This goes against logical retrosyntheticplanning (instead of finding good retrosynthetic disconnections you look forgood "add bond" connections) and even the parameters for measuringagainst the ideal synthesis, but the goal of this presentation is to learn whensuch intermediates might be strategic.
Notes:-I only care about making and cleaving C-C bonds.-Using DA/retro-DA to protect olefins doesn't count because I say so andbecause it is not interesting.-No degradation of commercially available SM. Make the complexity andthen destroy it (there may be one exception in this presentation).-This is not meant to be a bashing party. There are lots of both good andbad examples here. We can learn from both types.-By nature we must somehow fragment extraneous bonds in overbredintermediates, so I consider this topic a subset of Shenvi's 2005"Fragmentation Reactions in Synthesis" group meeting.