Diallyl substrates

The dichloro-dodecatriene-ruthenium complex is a highly efficient catalyst for the one-pot internal redox process that converts allylic alcohols (RC=C-C(OH) into carbonyl compoimds (RC-C-C=0, ketones or aldehydes) in the presence of CSCO3 imder N2 with high yields and turnover frequencies (TOP) in THF or H2O [Cadiemo et al. Chem Commun 232 2004, see also van der Drift et al. J Organomet Chem 650 1 2002]. It is also an efficient catalyst for the de-protection of V-allylic and V-diallylic substrates (with 3mol% of Ru) in aqneons solntion at... 

We now discuss an important case of the Cy5/Cy6 cyclization. Here the process begins with the intermolecular free radical addition of a free radical (Y ) to a diallylic substrate with the formation of an unsaturated radical (A") (Scheme 25). 

The first relevant report of a selective cyclization toward the (Cy 5) radical from a diallylic substrate was made in 1964 by Brace in the free radical chain reaction of 1,6-heptadiene (Scheme 25, X = CHj) with 1-iodoperfluoropropane initiated by AIBN. Further work, mainly by this author, confirmed (Scheme 25) the high selectivity toward formation of the (Cy 5) radical, in complete agreement with the results obtained with the 5-hexenyl radical (Sections II. 1 and III.1). Thus all reports, particularly in the polymerization area, that assumed formation of (Cy6) compounds must be regarded as suspect For instance, Cadogan and Hey reported the formation of a Cy5/Cy6 mixture by radical-initiated addition of various addenda to ethyl diallylacetate (X = CHCOjEt) but had to recognize later that the two compounds were in fact the two stereoisomeric (Cy5) compounds. 

Pyridine complexes of Pd- and Pt-pincer ligands are also suitable substrates for olefin metathesis [116]. The first-generation catalyst 9 efficiently mediates the RCM of diallylphosphines and diallyl sulfide when the heteroatom is com-plexed by a cationic [C5H5(NO)(PPh3)Re] moiety [117]. This principle has been exploited in the same study for tungsten, rhodium, and platinum complexes. 

When diallyl diazomalonate or allyl aryldiazoacetates are used as substrates in the rhodium-catalyzed reaction with di(tert-butyl)thioketene, 4-allyl-l,3-oxathiolan-5-one derivatives of type 158 are formed (82). After the initial 1,5-dipolar electro-cyclization, 157a undergoes a subsequent Claisen rearrangement to give the thermodynamically more stable compound 158 (Scheme 5.47). 

Ammonia fails to act as an effective nucleophile for 7r-allylpalladium complexes. Some examples of primary amines81-181-183 have been reported, although diallylation is often a problem in these reactions. Secondary amines are, however, excellent substrates for palladium-catalyzed allylation.81-84,181-183-195 Amides,176-196 sulfonamides,196-197 azides198 and magnesium amides199 have also been shown to be effective nucleophiles. 

A sequence of reactions that was recently reported by Hanessian and Alpegiani nicely illustrates how the allylstannane method is useful for functionalization of complex, sensitive substrates and, more generally, how stereochemistry can be controlled in radical addition reactions (Scheme 40).138 Dibromo- 3-lac-tam (25) can be monoallylated with a slight excess of allyltributylstannane and then reduced with tributyltin hydride to provide 3-allylated (3-lactam (26) (the acid salt of which shows some activity as a 3-lactamase inhibitor). Stereochemistry is fixed in the reduction step hydrogen is delivered to the less-hindered face of the radical. Alternatively, monodebromination, followed by allylation, now delivers the allyl group from the less-hindered face to provide stereoisomer (27). Finally, allylation of (25) with excess allylstannane produces the diallylated product (not shown). 

Primary alcohols have been successfully used as substrates for lipases. Monterde et. Al60 reported the resolution of the chiral auxiliary 2-methoxy-2-phenylethanol 1 via Candida antarctica lipase B (CAL-B)-catalyzed acylation using either vinyl acetate (R=H) or isopropenyl acetate (R= CH3) as acyl donor (cf. fig. 8) and the alkoxycarbonylation using diallyl carbonate as the alkoxycarbonylation agent in THF at 30 °C (cf. fig. 9). 

In accessing chiral allyl vinyl ethers for Claisen rearrangement reactions, Nelson et al. employed the iridium-mediated isomerization strategy. Thus, the requisite enantioenriched diallyl ether substrate 28 was synthesized via a highly enantioselective diethylzinc-aldehyde addition protocol10 (Scheme 1.1k). The enantioselective addition of Et2Zn to cinnamaldehyde catalyzed by (—)-3-exo-morpholinoisobomeol (MIB 26)11 provided an intermediate zinc alkoxide (27). Treatment of 27 with acetic acid followed by 0-allylation in the presence of palladium acetate delivered the 28 in 73% yield and 93% ee. Isomerization of 28 with a catalytic amount of the iridium complex afforded the allyl vinyl ether... 

The formation of sulfenyl carbanions is facilitated when the substrate contains a suitably positioned second sulfur atom or double bond, as in the case of dithians (see Chapter 3, p. 31) or allyl sulfides (46). The latter are thus easily converted into carbanions which can then be alkylated, and this provides a convenient procedure for coupling allyl groups for example, the allyl sulfide (46) can be transformed into diallyl (47) (Scheme 23). 

The enhancement of the enantiomeric excess of the mono-epoxide can be expected also in the epoxidation of the meso-secondary diallylic alcohol 31. Epoxidation of 32 gives the desired anfi-epoxide of high enantiomeric excess in good yield [72]. However, some meso-substrates bearing two hydroxy groups in close vicinity to each other may show unusual stereochemistry as discussed in the preceding section. 

Meldrum s acid derivatives have been shown to react with allylpalladium complexes derived from a variety of palladium sources. Several types of allylic acetates have been used as substrates, and the major product in these reactions is the diallyl Meldrum s acid derivative (e.g. (29)), often formed exclusively (Equation (12)). This and other metal-mediated reactions of Meldrum s acid and its derivatives are thoroughly discussed in a review <91H(32)529>. 

In a formal synthesis of brefeldin A, treatment of the allyl propargyl ether 305 with the base n-BuLi promoted deprotonation a- to the alkyne, followed by rearrangement to give predominantly the homoallylic alcohol 306 (3.199). " Likewise, deprotonation and rearrangement of the macrocyclic substrate 307 promoted rearrangement to the homoallylic alcohol 308, used in a synthesis of the diterpene kallolide B (3.200). Regioselective deprotonation of the diallyl ether 309 and... 

---