Nickel-Catalyzed Coupling Reaction of 1,3-Disubstituted Secondary Allylic Carbonates and Lithium Aryl- and Alkenylborates

Abstract

This account describes coupling reaction of 1,3-disubstituted secondary allylic carbonates with lithium aryl-and alkenylborates in the presence of a nickel catalyst. Borates examined are 4, 5, and 6, and reactivity and selectivity were investigated using the allylic carbonates 1a and 1b. Coupling of 1a,b with borates 4 was effected with the nickel catalyst, NiCl 2 (PPh 3 ) 2 or NiCl 2 (dppf), in THF at 45-65°C to provide products 3 in good yields with almost 100% regio-and stereoselectivities. Trivalent organoboranes prepared from acetylenes by hydroboration with catecholborane also underwent coupling reaction with 1a,b after transformation to borates 5 with MeLi. Though coupling using 4 and 5 required elevated temperature (45-65°C), cyclic borates 6 prepared in situ from boronates 8 and MeLi were found to couple with 1a,b at room temperature or below. Regio-and stereoselectivities were almost 100% as were observed in the cases of 4 and 5. In these reactions, palladium complexes such as Pd(PPh 3 ) 4 , Pd 2 (dba) 3 ‚CHCl 3 + 2 PPh 3 showed no catalytic activity. Stereochemical aspect of the present reaction was studied using cyclohexenyl carbonate 24 with 2-furylborate 4e and phenylborate 6a, and was found to proceed with overall anti fashion. With additional experiments, the mechanism of the present reaction was discussed in terms of transient π-allylnickel intermediates.

Palladium‐Catalyzed DYKAT of Butadiene Monoepoxide: Enantioselective Total Synthesis of (+)‐DMDP, (−)‐Bulgecinine, and (+)‐Broussonetine G

“…Allylic alkylation is known to be catalyzed by a variety of transition-metal complexes, including iron, [3] cobalt, [4] nickel, [5] molybdenum, [6] ruthenium, [7] rhodium, [8] palladium, [2] iridium, [9] tungsten, [10] and platinum. [11] Palladium has thus far proven to be the most versatile metal catalyst for AAA transformations.…”

Ruthenium‐Catalyzed Synthesis of Allylic Alcohols: Boronic Acid as a Hydroxide Source

“…[10] To expand the scope of nucleophiles in catalytic processes involving ruthenium complexes, we attempted the reaction of cinnamyl carbonate with phenylboronic acid. The expected product, which results from the transfer of a phenyl group through a classical transmetalation from boron to a transition metal, [11,12] was not formed, and only the branched and linear allylic alcohols were isolated as shown in Scheme 1. To the best of our knowledge, this reaction which corresponds to the delivery of an hydroxy group via a boron intermediate was unprecedented in the literature.…”

Arylation of 8-Acetoxyoctalenone in a Nickel-Catalyzed Coupling Reaction with Lithium Arylborates

“…Initially, installation of a phenyl group was examined using several organometallic compounds based on Zn, [6] Sn, [7] and B, [8] which are highly reactive toward allylic esters in the presence of appropriate catalysts, and the results are summarized in Table 1. When PhZnCl (7), prepared from PhLi and ZnCl 2 , was allowed to react with a stereoisomeric mixture of acetate 4α (α-OAc) and 4β (β-OAc) (4α/4β ϭ 1:3) in the presence of a palladium or a nickel catalyst under Negishi's conditions, [6] a mixture of unidentified products (Entry 1) or the reduction compound 3 was obtained as a major product (Entry 2), respectively.…”

“…Finally, the borate reagent was examined, which is reactive toward allylic esters only in the presence of a nickel catalyst. [8] Reaction of phenylboronate ester 12a (Ar ϭ Ph) and nBuLi [11] at room temperature for 15 min generated lithium phenylborate 10a in situ, and further reaction with acetate 4 at 60°C afforded 11a (Ar ϭ Ph) as a major product, for the first time (Entries 4Ϫ6).…”

“…The boronate esters 12d,e [p-PhC 6 H 4 , p-N(Me 2 )C 6 H 4 ] were prepared in 94 and 50% yields, respectively, by the method [8] for synthesis of 12b,c (Ar ϭ p-MeC 6 H 4 , p-MeOC 6 H 4 ) through lithiation of the corresponding aryl bromides followed by reaction with B(OiPr) 3 and esterification with 2,3-butanediol. As sumScheme 1.…”