Construction of a quaternary carbon at the carbonyl carbon of the cyclohexane ring

Kaneko, Yuki; Kiyotsuka, Yohei; Acharya, Hukum P.; Kobayashi, Yuichi

doi:10.1039/c0cc00653j

Cited by 33 publications

(39 citation statements)

References 9 publications

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“…The resulting mixture was extracted with EtOAc three times. The combined extracts were washed with brine, dried over MgSO 4 , and concentrated to afford a residual oil, which was purified by chromatography on silica gel (hexane/EtOAc) to afford selenide 11 (1.09 g, 90 %). (1S,4S,5S)-4-(4-Methoxyphenyl)-6,6-dimethylbicyclo-[3.1.1]heptan-2-one (13): 7% H 2 O 2 (2.09 mL, 4.24 mmol) was added to an ice-cold solution of selenide 11 (841 mg, 2.87 mmol) and pyridine (0.46 mL, 5.70 mmol) in CH 2 Cl 2 (6 mL).…”

Section: Methodsmentioning

confidence: 99%

“…The resulting mixture was extracted with EtOAc three times. The combined organic layers were washed with brine, dried over MgSO 4 , and concentrated to afford a residual oil, which was purified by chromatography on silica gel (hexane/ EtOAc) to give ketone 13 (581 mg, 83 % from 11). NaH (80 mg, 60 % in mineral oil, 2.01 mmol) was added to a solution of the above acetate in MeOH (10 mL) at RT.…”

Section: Methodsmentioning

confidence: 99%

“…The resulting mixture was extracted with CH 2 Cl 2 three times. The combined extracts were washed with saturated CuSO 4 and brine, dried over MgSO 4 , and concentrated to afford enone 12, which was used for the next reaction without further purification. Enone 12: pMeOC 6 H 4 MgBr (8.0 mL, 0.90 m in THF, 7.20 mmol) was added dropwise to a suspension of CuI (328 mg, 1.72 mmol) in THF (8 mL) at À78 8C and the solution was stirred at À78 8C for 30 min.…”

Section: Methodsmentioning

confidence: 99%

“…A solution of the above enone 12 in THF (8 mL) was added dropwise. The mixture was allowed to warm to À50 8C over 2 h and saturated NH 4 Cl was added. The resulting mixture was extracted with EtOAc three times.…”

Section: Methodsmentioning

confidence: 99%

“…[4] The stereochemistry is controlled by the equatorial attack of reagents to the allylic end (S N 2' position) in the thermodynamically stable chair conformer, which creates a quaternary carbon center with the axial vinyl and equatorial alkyl groups. We supposed that the cyclohexane I with Ar (pMeOC 6 H 4 ) and R 1 (Me 2 C(OH)or CH 2 = C(Me)) in equatorial positions is the most stable conformer, and that allylation of I with a methyl copper reagent would produce II, in which the quaternary carbon center in 1 and 3 is correctly furnished (Scheme 1).…”

Section: Introductionmentioning

confidence: 99%

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Synthesis of Cyclobakuchiols A, B, and C by Using Conformation‐Controlled Stereoselective Reactions

Kawashima

Kaneko

Sakai

et al. 2013

Chemistry A European J

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Cyclohexanone with the pMeOC6H4 and CH2=C(Me) substituents at the C3 and C4-positions was prepared from (+)-β-pinene and converted to the allylic picolinate by a Masamune-Wittig reaction followed by reduction and esterification. Allylic substitution of this picolinate with Me2CuMgBr·MgBr2 in the presence of ZnI2 proceeded with γ regio- and stereoselectively to afford the quaternary carbon center on the cyclohexane ring with the CH2=CH and Me groups in axial and equatorial positions, respectively. This product was converted to cyclobakuchiol A by demethylation and to cyclobakuchiol C by epoxidation of the CH2=C(Me) group. For the synthesis of cyclobakuchiol B, the enantiomer of the above cyclohexanone derived from (-)-β-pinene was converted to the cyclohexane-carboxylate, and the derived enolate was subjected to the reaction with CH2=CHSOPh followed by sulfoxide elimination to afford the intermediate with the quaternary carbon center with MeOC(=O) and CH2=CH groups in axial and equatorial positions. The MeOC(=O) group was transformed to the Me group to complete the synthesis of cyclobakuchiol B.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Synthesis of Cyclobakuchiols A, B, and C by Using Conformation‐Controlled Stereoselective Reactions

Kawashima

Kaneko

Sakai

et al. 2013

Chemistry A European J

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Reversing the Stereoselectivity of a Palladium‐Catalyzed O‐Glycosylation through an Inner‐Sphere or Outer‐Sphere Pathway

Xiang

Hoang

et al. 2014

Angewandte Chemie

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An efficient and concise method for the construction of various O-glycosidic bonds by a palladium-catalyzed reaction with a 3-O-picoloyl glucal has been developed. The stereochemistry of the anomeric center derives from either an inner-sphere or outer-sphere pathway. Harder nucleophiles, such as aliphatic alcohols and sodium phenoxides give bproducts, and a products result from using softer nucleophiles, such as phenol.Recent advances in our understanding of the indispensable roles of carbohydrates in all major life forms over the past decades have generated a great demand to synthesize these complex biomolecules. Hence, efficient glycosylation methods through the usage of little to no activators are highly sought after, especially one that offers high yields and stereoselectivities.[1] At present, palladium-catalyzed O-glycosylation [2] with glycals as donors [3][4][5] has received less attention compared to traditional glycosyl donors, [6] mainly because of the difficulty in generating the palladium/p-allyl intermediates from the electron-rich glycal scaffold and the low reactivity. [7] Recent reports focused on the use of trichloroacetimidate [8] as a directing group [9] and a zinc reagent [10] was chosen to soften the O-nucleophiles (Scheme 1 a). However, the rearrangement by-products [3b, 11] reduced the yields and additives often complicate the reaction process. Another promising directing group was O-picoloyl which is reported to strongly coordinate metal centers [12] as well as undergo selective glycosylation with pyranosyl donors through hydrogen-bond assistance (Scheme 1 b). [13] In the majority of palladium-catalyzed glycosylation reactions, the selectivity could be controlled by either the nature of the ligand [3a] or palladium source. [14] In contrast, the poor affinity of the O nucleophile for the metal center also played an important role in the stereochemical outcome. As demonstrated by Tsuji and Trost, [15] softer nucleophiles prefer an outer-sphere mechanism in which nuclephilic substitution from opposite face of palladium complex is the dominant pathway. Harder nucleophiles, on the contrary, directly attack the metal center with subsequent reductive elimination to form the product (Scheme 1 c).[16] To investigate the effect of the above factors in the reaction with a specific glycal system, we proposed a palladium-catalyzed glycosylation strategy with an O-picoloyl moiety as a directing group at the C3-position of a glycal-type donor (Scheme 1 d).First, the picoloyl glucal donor 1 was prepared from 4,6-O-(para-methoxy)benzylideneglucal and picolinic acid. For optimizing the reaction conditions, the soft nucleophile 3,4,5-trimethoxyphenol (2 a) was chosen as the acceptor.[17]The reaction was expected to proceed through an outersphere pathway with the palladium approaching the allylic system from the b face. Hence, the a-product 3 a should be the major isomer (see Scheme 2). The optimized reaction conditions with soft nucleophiles, that is, phenols, were found to be 10 % [Pd(PPh 3 ) 4...

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Reversing the Stereoselectivity of a Palladium‐Catalyzed O‐Glycosylation through an Inner‐Sphere or Outer‐Sphere Pathway

Xiang¹,

Hoang²,

He³

et al. 2014

Angew Chem Int Ed

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Construction of a quaternary carbon at the carbonyl carbon of the cyclohexane ring

Abstract: High S(N)2' selectivity in the allylic substitution of cyclohexylidene ethyl picolinates with copper reagents prepared from RMgBr and CuBr.Me(2)S was realized by addition of ZnX(2) (X = I, Br, Cl). Furthermore, ZnX(2) accelerated the reaction with the bulky iPr reagent.

Cited by 33 publications

References 9 publications

Synthesis of Cyclobakuchiols A, B, and C by Using Conformation‐Controlled Stereoselective Reactions

Synthesis of Cyclobakuchiols A, B, and C by Using Conformation‐Controlled Stereoselective Reactions

Reversing the Stereoselectivity of a Palladium‐Catalyzed O‐Glycosylation through an Inner‐Sphere or Outer‐Sphere Pathway

Reversing the Stereoselectivity of a Palladium‐Catalyzed O‐Glycosylation through an Inner‐Sphere or Outer‐Sphere Pathway

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