Dimethyl diallylmalonates

Palladium-catalyzed enantioselective hydrosilylation of carbon-carbon double bonds is well known." Widenhoefer s group recently extended this reaction to cyclization of functionalized 1,6-dienes. The PyrOx ligands were excellent ligands for this reaction, and comparative evaluations of ligand performance for the hydrosilylation-cyclization of dimethyl diallylmalonate 613 have been reported (Scheme 8.193)." ° " The trans-isomer of 614 is the preferred product and... 

Widenhoefer and co-workers have developed an effective Pd-catalyzed protocol for the asymmetric cyclization/ hydrosilylation of functionalized 1,6-dienes that employed chiral, non-racemic pyridine-oxazoline ligands." " " Optimization studies probed the effect of both the G(4) substituent of the pyridine-oxazoline ligand (Table 7, entries 1-6) and the nature of the silane (Table 7, entries 6-15) on the yield and enantioselectivity of the cyclization/ hydrosilylation of dimethyl diallylmalonate. These studies revealed that employment of isopropyl-substituted catalyst (N-N)Pd(Me)Gl [N-N = (i )-( )-4-isopropyl-2-(2-pyridinyl)-2-oxazoline] [(i )-43f and a stoichiometric amount of benzhydryldimethylsilane provided the best combination of asymmetric induction and chemical yield, giving the corresponding silylated cyclopentane in 98% yield as a single diastereomer with 93% ee (Table 7, entry 15). 

Dimethyl bis-benzamidinato complex, with Ti(IV), 4, 344 Dimethyl carboranes, with tantalum, 5, 163 Dimethyl complexes with cadmium, 2, 464 with nickel, 8, 58-59 with platinum(II), 8, 460 with titanium(IV), 4, 331, 4, 343 Dimethyl diallylmalonate, cyclization-hydrosilylation, 11, 385 Dimethyl diamido complexes, with Ti(IV), 4, 332... 

The ideal substrates for these reactions are 1,6-dienes [37-38], for example (Scheme 7), dimethyl diallylmalonate is easily transformed into cyclopentane derivatives, as a mixture of cis and trans isomers. The methodology also applies to analogous enynes [39-40], diynes [41], or eneallenes [42]. The radical acceptor in the cyclization step can even be an imino group [43a-c], or a nitrile [43d]. 

As an extension of hydrosilylation of alkenes, cyclization-hydrosilylation of 1,6-dienes occurs by the reaction with HSiRs [23]. The cationic complex 37, generated in situ from (phen)Pd(Me)Cl and NaBAr4, is an active catalyst, catalyzing the reaction of dimethyl diallylmalonate (36) with HSiCl3 to give the disubstituted cyclopentane 38 with 98% trans selectivity in 92% yield [24]. A mechanism different from that of usual hydrosilylation, which postulates formation of H-Pd-SiR3 and hydropalladation of alkene, was proposed by Widenhoefer... 

Silylcarbocyclization of Dienes. The Pd-catalyzed silylcarbocyclizations of 1,6- and 1,7-dienes (30,41-49) have been extensively studied. The reaction of dimethyl diallylmalonate 33 with EtsSiH catalyzed by [(phen)PdMe(0Et)2]" "-BAr4 gave trans-disubstituted cyclopentane 34 in 93% yield (Scheme 17) (41). 

Thiol-promoted cyclization of 1,6-dienes and analogous enynes in the presence of radical initiators has been studied. An equimolar amount of ethanethiol, in the presence of diphenyl disulfide as initiator, was added under photolytical conditions to dimethyl diallylmalonate an addition of thiyl radical followed by 5-hex-enyl cyclization took place [48] and cis- and fra 5-cyclopentanes (the ratio being... 

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