Reactivity of Organocerium Compounds with Allyl Alcohols

Mechanism and Extensibility of the Reaction

“…[4] These findings As shown in Table 1, the reaction works well with both open up an interesting and new window on the synthetic allyl (entries 1Ϫ12) and propargyl alcohols (entries 13Ϫ15) application of organocerium reagents which, until now, with a large variety of substituents at the positions R 1 , R 2 were employed mainly in the addition to electrophilic and R 3 . Among the organocerium species, the most remarkable finding from this reaction is the addition of hy- [4] framework of the organocerium reagent binds to the double might be tentatively described as [(R 4 ) 3 CeCl 2 ORЈ] 3Ϫ or [(R 4 ) 3 CeORЈ] Ϫ (A, Scheme 1). bond terminus farthest from the alcohol function, while with R 1 ϭ aryl (entries 9Ϫ14), it is linked to the nearest Species such as [R 4 Ce(ORЈ) 3 ] Ϫ and the addition of R 4 Li one.…”

“…The equivalent is required. [4] only reported complete reduction of an unsaturated compound is the formation of 3-(2-hydroxyphenyl)-1-propanol Coordination to the oxygen atom of the cerium species, in analogy with the proposal of Eisch for lithium or mag-from the cerium-mediated lithium aluminum hydride reduction of coumarin (Equation B, Scheme 2). [10] This result nesium, [2] should be the key intermediate step in the reaction.…”

“…The reaction was carried out as reported previously, [4] give a noncyclic dianonic species. The second mechanism i.e.…”

“…It has The optimum reaction conditions require a molar ratio of been reported that Ce(ORЈ) 3 species are able to form "ate" 1:1:3 for alcoholate, cerium trichloride and organolithium complexes at Ϫ78°C. [6] [8] However, the preparation of cereagent, while a molar ratio of 1:1:1 leaves large amounts rium octen-3-olate (7a) at room temperature, in analogy of unreacted starting materials, [4] thus indicating that the with MehorotraЈs procedure for lanthanide alcoholates, [9] "R 4 CeCl 2 " species commonly reported in the reaction of followed by addition of butyllithium (1:3:3 cerium trichloorganocerium reagents [5k] cannot be the reactive species. ride/alcoholate/butyllithium ratio) at Ϫ78°C gave no reac-Denmark has reported that an [(R 4 ) 3 CeCl 3 ] 3Ϫ species may tion.…”

“…While the aliphatic oxygen is al-Scheme 1. General mechanism of the reaction ready busy, the aromatic one may form an "ate" complex R 1 is an alkyl group, the "ate" complex transfers the R 4 alkyl group to the farthest terminus of the double bond similar to A (C, Scheme 2) which should promote the second addition of hydride. Moreover, we have found the for-(Scheme 1, pattern a).…”