Double Diels-Alder Tethers

Regiochemistry of Multiple Additions 10.3.3.4 Double Diels-Alder Tethers... 

Scheme 10.26 Regioselective tethered double Diels-Alder-additions to Q,...

Formation of Bis-adducts by Double Diels-Alder Addition of Tethered Bis(buta-l,3-diene)s to C o... 

Nishimura and co-workers used bis(o-quinodimethanes) connected by a.n+dioxa-methylene tethers for the regioselective bis-functionalization by double Diels-Alder addition (Scheme 7-14) [93]. The tethered bis(o-quinodimethanes) were intermediately formed by heating the bis(bromomethyl) derivatives 72a-d together with C, in toluene in the presence of KI and [18]crown-6 [90]. With an 0-(CH2)2-0 tether (72a), the cis-2 and cw-3 bis-adducts 73a and ( )-74a were isolated in 10% and 8% yield, respec-... 

Scheme 7-14 Regioselective bis-functionalizations by double Diels-Alder addition of tethered bis(o-quinodimethanes) to Cgo [93, 94].

B, which first undergoes a carbene addition. Heating the adduct promotes a double Diels-Alder reaction, and the constraints provided by the tethers direct the reactions such that a 60% )field of the single adduct shown can be obtained. Many variants of this strategy have been developed. 

Weinreb reported the intramolecular Diels-Alder reaction of oximino malonates tethered to a diene 268 under high dilution conditions. The cycloaddition adduct 269 underwent double eliminations with cesium carbonate to afford the pyridine 270. 

The intramolecular Heck reaction followed by a Diels-Alder cycloadditiont leading to bicyclo[4.3.0]nonene derivatives has been developed into a one-pot cascade reaction.f f Various 2-bromo-l,6-heptadienes including systems with heteroatoms in the tether between the double bonds were cyclized under palladium catalysis producing vicinal exodimethylenecycloalkanes, which reacted with dienophiles (either present... 

An intramolecular hetero Diels-Alder reaction of a,a-dioxosulflnes with a tethered electron-rich double bond 47, generated in situ, affords the bicychc adduct 48 . 

Slee and LeGoff performed further investigations on the reaction of dimethyl acetylenedicarboxylate 4-20 with an excess of furan 4-21, as first described by Diels and Alder (Scheme 4.5) [la]. At 100 °C, 4-24 and 4-25 were not produced (as proposed), but rather 4-22 and 4-23, since at elevated temperature an equilibrium takes place and the primarily formed 4-24 and 4-25 isomerize to give a 6 1-mixture of the exo-endo and the exo-exo products 4-22 and 4-23, respectively. However, at lower temperature, in the primarily formed [4+2] cycloadduct the double bond substituted with the two carbomethoxy group acts as the dienophile to give the two products 4-24 and 4-25 in a 3 1 ratio with 96% yield within five weeks, as has been shown by Diels and Olsen [la,lc]. For a differentiation of these two types of adducts, Paquette and coworkers [7] used a domino and pincer product . The Cram group [8] described one of the first examples of a reaction of a tethered bisfuran 4-26 with dimethyl acetylenedicarboxylate 4-20a to give 4-27. 

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