Oxypalladation alcoholic groups

Propargylic alcohol, after lithiation, reacts with CO2 to generate the lithium carbonate 243, which undergoes oxypalladation. The reaction of allyl chloride yields the cyclic carbonate 244 and PdC. By this reaction hydroxy and allyl groups are introduced into the triple bond to give the o-allyl ketone 245[129]. Also the formation of 248 from the keto alkyne 246 with CO2 via in situ formation of the carbonate 247 is catalyzed by Pd(0)[130]. 

An interesting variant involves the use of an allylic alcohol as the alkene component. In this process, re-oxidation of the catalyst is unnecessary since the cyclization occurs with /Uoxygen elimination of the incipient cr-Pd species to effect an SN2 type of ring closure. Both five- and six-membered oxacycles have been prepared in this fashion using enol, hemiacetal, and aliphatic alcohol nucleophiles.439,440 With a chiral allylic alcohol substrate, the initial 7r-complexation may be directed by the hydroxyl group,441 as demonstrated by the diastereoselective cyclization used in the synthesis of (—)-laulimalide (Equation (120)).442 Note that the oxypalladation takes place with syn-selectivity, in analogy with the cyclization of phenol nucleophiles (1vide supra). 

Intramolecular cyclization of alcohols to 1,3-dienes can lead to fused tetrahydrofurans and tetrahydropyrans. In this reaction, using 5 mol% Pd(0Ac)2, the first step involves a trans oxypalladation to form the heterocyclic ring and a jr-allyl palladium complex. In the presence of 0.2 equiv. of LiCl, AcO adds trans to the r-allyl, leading to a net cA-l,4 addition of oxygen nucleophiles to the diene. When LiCl is omitted, the AcO adds to the same face of the r-allyl as the palladium, giving net tra/ 5-1,4-addition of oxygen groups to the diene (Scheme 41). 

Carbonylation of alkenes having an amino or hydroxy group (AH or BH = OH or NHR) 140, 142 and 144 offers interesting synthetic methods for cyclic compounds. The 4-pentenylamine or alcohol 140 is converted to 141 via amino or oxypalladation, followed by carbonylation. The amino alcohol 142 gives 143 by palladation and carbonylation by path a. The homoallylic amine or alcohol 144 is converted to lactone or lactam ester 145 by path c [60]. 

A similar experiment with an unsaturated alcohol reported by Stoltz also implies that syn oxypalladation occurs. Again, the observation of deuterium in the product implies that the alkoxyalkylpalladium intermediate contains the palladium cis to the alkoxo group and trans to the deuterium label. The stereochemical outcome of catalytic cyclizations reported by Wolfe also imply that cis oxypalladation occurs during certain transformations, as shown in Equation 9.82. 

Cyclization of homoallylic alcohols bearing an OH group at the allylic position gives an oxypalladation intermediate in which the OH group is in the adjacent position of Pd—C bond. In such cases, elimination of Pd—OH predominates to give dihydrofurans as shown in Scheme 34.The same type of cyclization and elimination occurs with /3-diketones bearing allylic alcohol moiety. The cyclization proceeds via keto-enol tautomerism (Scheme 35). 

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