New Chiral Molybdenum Catalysts for Asymmetric Olefin Metathesis that Contain 3,3‘-Disubstituted Octahydrobinaphtholate or 2,6-Dichlorophenylimido Ligands

Abstract

octahydro-1,1′-bi-2-naphthol was derivatized with mesityl and benzhydryl groups in the 3 and 3′ positions to give R-H 2 Mes 2 Bitet and R-H 2 -Benz 2 Bitet, respectively. Addition of R-K 2 Benz 2 Bitet to Mo(NAr)(CHCMe 2 Ph)(OTf) 2 (dme) yielded Mo(NAr)(CHCMe 2 Ph)(R-Benz 2 Bitet)(THF) (7), while addition of R-K 2 Mes 2 Bitet to Mo(NAr)(CHCMe 2 Ph)(OTf) 2 (dme) in THF gave Mo(NAr)(CHCMe 2 Ph)(R-Mes 2 Bitet)(THF) (8). Four complexes that contained the 2,6-dichlorophenylimido ligand were prepared by similar procedures, namely, Mo(NAr Cl )(CHCMe 3 )(S-Biphen)(THF) (9), Mo(NAr Cl )(CHCMe 3 )(R-Trip 2 -BINO)(THF) (10), Mo(NAr Cl )(CHCMe 3 )(R-Mes 2 Bitet)(THF) (11), and Mo(NAr Cl )(CHCMe 3 )-(R-Benz 2 Bitet)(THF) (12). X-ray studies of 8, 9, and 12 revealed them to be typical distorted trigonal bipyramids with THF and one biphenolate oxygen occupying axial positions. In 9 and 12 the alkylidene orientation was found to be syn, while in 8 the alkylidene orientation was found to be anti. Catalysts 7, 8, 9, 10, 11, and 12 were all efficient in terms of both conversion and % ee for two standard desymmetrization reactions to form dihydrofurans.

Molybdenum Imido Alkylidene Metathesis Catalysts That Contain Electron-Withdrawing Biphenolates or Binaphtholates

“…15 In fact, the only other isolated THF adduct of a [Biphen] 2− complex is Mo(N-2,6-Cl 2 C 6 H 3 )(CHCMe 2 Ph)(Biphen)(THF), since the N-2,6-Cl 2 C 6 H 3 ligand creates a more electrophilic metal center. 16 Coordination of THF in 5a is also consistent with a more electrophilic metal center than that in Mo(NAr)(CHCMe 2 Ph)(Biphen).…”

“…The overall structure is analogous to that shown in Figure 2 and all bond angles and bond distances observed are typical for five-coordinate complexes of this type (see caption to Figure 5). 16 Mo(NR)(CHCMe 2 Ph)(Biphen CF3 )(THF) complexes (R = Ar′ (5b) or R = Ad (5c); equation 5) were prepared in a manner analogous to the synthesis of 5a. The 1 H NMR spectrum of 5b in C 6 D 6 showed it to be a mixture of anti (14.10 ppm, J CH =146 Hz, ~75%) and syn isomers (12.41 ppm, J CH = 117 Hz, ~ 25 %).…”

The Development of the Asymmetric Morita—Baylis—Hillman Reaction Catalyzed by Chiral Brønsted Acids

“…Saturation of the BINOL derivatives and substitution at the 3,3'-positions (entries 3 -5 and 9 -13) led to higher enantioselectivities. The highest levels of enantioselectivity were achieved with (R)-3,3'-diaryl-H 8 -BINOL derivatives, with the exception of the 3,3'-dimesityl-catalyst 8e, [20] which afforded the product in low enantioselectivity, 31% ee, and low yield (entry 12). It was postulated that the mesityl ortho-methyl groups restrict rotation about the biaryl bond of the 3-substituent and the binaphthalene core which must be a requirement for high yield and enantioselectivity.…”

“…[19] Compounds 5c and 8e were synthesized according to the literature procedure. [20] The absolute configurations of products 2a and 2j were determined by comparison to known products. [19] Other absolute configurations were assigned through analogy.…”

“…The addition of bromine at À 30 8C gave the 3,3'-dibromo cross-coupling partner 9 in 94% yield. [20] Using Suzuki reaction conditions as reported by Fu [23] or Snieckus [24] yielded the corresponding (R)-3,3'-diaryl-H 8 -BINOMe compounds 10a -d. Deprotection of the methyl ethers with boron tribromide at 0 8C gave catalysts 8a, b,d. Demethylation of 10c with boron tribromide was performed at À 78 8C to À 20 8C in order to avoid bromination of the highly activated 3,5-(bis-trifluoromethyl)phenyl group [25] yielding catalyst 8c.…”