Carbonates, allylic, coupling

The spectra fit the ester structure well, but not the more symmetrical diketone structure at all. There are three types of proton (cyclobuta-l,3-dione would have just one) with allylic coupling between one of the protons on the double bond and the CH2 group in the ring. The carbonyl group has the shift (185 p.p.m.) of an acid derivative (not that of a ketone which would be about 200 p.p.m.) and all four carbons are different. 

Similarly palladium-catalyzed nucleophilic allylic coupling of 1-vinylcyclopropan-l-ol and its derivatives with stabilized (soft) and nonstabilized (hard) carbon nucleophiles occurred regioselectively without ring opening of the three-membered ring to give, for example, 9. ... 

The palladium-catalysed coupling of allylic esters with carbanions has now been extended to include other reactions. The allylic carbonate 299 couples with the nitro compound 300 to give the expected product 301 in good yield. 

The double and triple resonance experiments with roxburghine-D establish that the hydrogen atom at 0-15 Hg) is coupled to two hydrogens at C-14 and one at C-20 but there is also a small coupling between Hb and the hydrogen atom (H2) at C-17 (t/ 15,17 = 0.6 Hz). Such an allylic coupling is reasonable on the basis of structure 80 but is much less easily rationalized on the basis of structure 81. Further, the chemical shifts observed for the protons at C-15 and C-20 (S 2.15 and 1.76, respectively) are consistent with an allylic position for the former and an attachment of C-20 to saturated carbon atoms only. 

There are a host of palladium-catalyzed C-C coupling reactions that have been developed since the mid-1960s, but only a couple of specific examples will be covered here (cf. Ref 14, 14a). Tsuji discovered Pd-catalyzed tr-allyl and carbon nucleophile coupling reactions in 1965.Mizoroki and Heck " separately developed vinylic coupling reactions (Equation (16)) in the early 1970s, and this is commonly referred to as a Heck reaction or coupling. 

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