Overman spirocyclization

During the same year, Overman and co-workers synthesized spirocycle 5.14 in 90% yield with 45% ee by two sequential Heck cyclization of trienyl triflate 5.13 at room temperature in the presence of Pd(OAc)2-(R,R)-DIOP and Et3N in benzene. 

A variety of different tactics have been used to establish all-carbon spirocyclic moieties at oxindole C3. Overman and Watson have conducted an extensive investigation of intramolecular Heck reactions leading to the diastereoselective formation of spirocyclic dioxindoles, e.g., Ill and 114 (Scheme 29) [67-69]. Interestingly, while sequential Heck cyclizations of acetonide protected bis-anilide... 

Formation of cyclobutanes is not conunon. As a rare example. Overman reported that w-cyclization of the triflate 209 afforded the spirocycle 211 as a major product via 210. At the same time, construction of the cyclobutane 213 by A-exo cyclization of 210 occurred and 214 was detected in 5 % yield [97]. 

Mizoroki-Heck reaction of 141 was usedby Overman and coworicers [68] in the synthesis of a phenolic aphidicolin analogue (143), affording the spirocyclic product 142 in good yield (67%), but with mediocre diastereoselectivity (141 142, Scheme 5.26). Further spirocyclic products (not shown) were synthesized by Ripa and Hallberg [30] in moderate yields (44-52%) (discussed in Section 5.2). 

Ashimori, A. and Overman, L.E. (1992) Catalytic asymmetric synthesis of quaternary carbon centers. Palladium-catalyzed formation of either enantiomer of spirooxindoles and related spirocyclics using a single enantiomer of a chiral diphosphine ligand. J. Org. Chem., 57, 4571-2. 

Ashimori, A., Bachand, B., Overman, L. E. and Poon, D. J. 1998b. Catalytic asymmetric synthesis of quaternary carbon centers. Exploratory investigations of intramolecular Heck reactions of ( )-a,P-unsaturated 2-HaloanUides and analogues to form enantioenriched spirocyclic products. J. Am. Chem. Soc. 120 6477-6487. 

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