Stereochemistry of the addition of a grignard reagent to terpene ketones with seven-membered rings

The dehydration of 1,2,5,5- and 1,2,6,6,-tetramethylcycloheptanols by the POCl₃/Py system has been studied. It has been established that the products of the dehydration of 1,2,5,5-tetramethylcycloheptanols are 1,2,5,5- and 1,4,4,7-tetramethylcycloheptenes, and those of the dehydration of 1,2,6,6-tetramethylcycloheptanols are 1,3,3,7- and 1,2,4,4-tetramethylcycloheptenes. On the basis of the results of dehydration by the POCl₃/Py system it has been shown that the Grignard reactions of 2,5,5- and 2,6,6-trimethylcycloheptanols form mainly tertiary alcohols with the trans orientation of the vicinal OH and CH₃ groups.     

Stereochemistry of the addition of a grignard reagent to terpene ketones with seven-membered rings

The dehydration of 1,2,5,5- and 1,2,6,6,-tetramethylcycloheptanols by the POCl₃/Py system has been studied. It has been established that the products of the dehydration of 1,2,5,5-tetramethylcycloheptanols are 1,2,5,5- and 1,4,4,7-tetramethylcycloheptenes, and those of the dehydration of 1,2,6,6-tetramethylcycloheptanols are 1,3,3,7- and 1,2,4,4-tetramethylcycloheptenes. On the basis of the results of dehydration by the POCl₃/Py system it has been shown that the Grignard reactions of 2,5,5- and 2,6,6-trimethylcycloheptanols form mainly tertiary alcohols with the trans orientation of the vicinal OH and CH₃ groups.Institute of Physical Organic Chemistry, Academy of Sciences of the Belorussian SSR, Minsk. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 432–436, July–August, 1986.     

Organocatalytic asymmetric alpha-bromination of aldehydes and ketones

The first organocatalytic enantioselective alpha-bromination of aldehydes and ketones is presented; a C2-symmetric diphenylpyrrolidine catalyst afforded the alpha-brominated aldehydes in good yields and up to 96% ee, while ketones were alpha-brominated by a C2-symmetric imidazolidine in up to 94% ee; furthermore, the organocatalytic enantioselective alpha-iodination of aldehydes is also demonstrated to proceed with up to 89% ee.     

Trifluoromethanesulfonic acid-catalyzed solvent-free bisindolylation of trifluoromethyl ketones

A trifluoromethanesulfonic acid-catalyzed solvent-free bisindolylation reaction of indoles with alkyl and aryl trifluoromethyl ketones has been developed. The trifluoromethyl-substituted bisindolylalkane derivatives were synthesized in moderate to excellent yields.     

One-pot synthesis of homoallylic ketones from the addition of vinyl grignard reagent to carboxylic esters

Fifteen homoallylic ketones have been synthesized in 26-77% yields on treatment of aromatic, aliphatic, and alpha-amino methyl carboxylates with excess vinylmagnesium bromide and catalytic amounts of a copper salt in THF. Alpha-amino homoallylic ketones derived from N-protected alpha-amino esters possessing aliphatic and alcohol side chains were synthesized in > or =98% enantiomeric purity. [reaction: see text]     

Reaction of a free organic radical with grignard reagent

Summary The behavior of a free organic radical 2,2,6,6-tetramethyl-4-piperidone oxide of nitrogen in a Grignard reaction was studied. The reaction with the Grignard reagent proceeded without affecting the free valence and led to a new organic radical with a tertiary hydroxyl group.     

Ionic liquid, surrogate hydrogen bromide reagent for ring opening of cyclopropyl ketones

Ionic liquid reagents created by addition of 1 equiv of either CF3CO2H or CF3SO3H to N-pentylpyridinium bromide exhibit excellent chemical reactivities as surrogate HBr reagents in ring-opening reactions of cyclopropyl ketones as well as of 2,2-difluorocyclopropyl ketones to form the respective 3-bromopropyl or 3-bromo-2,2-difluoropropyl ketones in good to excellent yields.     

Reaction of polyepichlorohydrin with magnesium and grignard reagents

The reaction of polyepichlorohydrin with magnesium in tetrahydrofuran at reflux temperature was studied in the hope of obtaining a polymeric Grignard reagent. The polymeric Grignard reagent could not be obtained, but dechlorination occurred. It was confirmed that the Grignard reagent of polyepichlorohydrin was formed as an intermediate during the dechlorination. The reactions of polyepichlorohydrin with Grignard reagents were carried out in tetrahydrofuran at reflux temperature. Benzylmagnesium chloride and allylmagnesium chloride were used as Grignard reagents. It was found that the chlorine atom in polyepichlorohydrin can be replaced by benzyl and allyl groups. The extent of the substitution increased with increasing concentration of Grignard reagent. Dechlorination and scission of the ether linkage occurred simultaneously as side reactions.     

Macrocycles with sulfide and amine binding sites as chiral ligands for nickel catalyzed cross coupling of a grignard reagent with vinyl bromide

Synthetic routes to macrocycles derived from (S)-phenyl alanine and (S)-cysteine have been developed. The catalyzed coupling of the Grignard reagent of 1-chloro-1-phenylethane and vinyl bromide in the presence of these ligands proceeds usually in good yields and in enantiomeric excesses (e.e.) of up to 46%.     

Preparation of functionalized ketones via low temperature grignard reaction

δ-Chloroketones and 5-oxo-9-decenoic acid methyl ester were prepared from 5-chlorovaleryl chloride and methyl 4-(chloroformyl)-butyrate via Grignard reaction in tetrahydrofuran at ?70°.     

Functionalized ketones by iron mediated reaction of grignard reagents with acyl chlorides

The iron(III)-catalyzed cross-coupling reaction between Grignard reagents and acyl chlorides was found to be widely applicable to the synthesis of various functionalized ketones in good yields under mild conditions; the series of examples includes the synthesis of chiral methyl ketones and symmetric diketones.     

Reactions of pyridyl and quinolyl sulfoxides with grignard reagent: A convenient preparation of pyridyl and quinolyl grignard reagents

3-,4-Pyridyl and 4-quinolyl Grignard reagents were generated by the reaction of the corresponding phenyl sulfoxides with PhMgBr and give the adducts upon treatment with various aldehydes and ketones. The stereochemistry for the reaction was investigated.     

双环戊二烯基二氯化钛催化下格氏试剂与偕二卤代烷的反应

本文作者进行了在双环戊二烯基二氯化钛催化下, 异丙基格氏试剂对偕二卤代烷的还原反应的研究, 这对扩大该催化还原体系的应用范围是有意义的。本文报道该反应的研究结果及可能的反应机理。     

Chemoselective preparation of ketones by the grignard reaction of N-acylpyrazoles

N-Acylpyrazoles afford chemoselectively the corresponding ketones in good yields by the use of equimolar amounts of Grignard reagent. In the case of an optically active N-acylpyrazole, optical asymmetry was retained in comparable optical yield. Ketone formation by the Grignard reactions can be regarded as an important functionalization in a synthetic loop using pyrazoles as the auxiliary compound.     

Reduction of halogenated ketones with magnesium haloalkoxides

The degree of thermal stability of magnesium haloalkoxycarbinolates containing thienyl groups and dichloro-, trichloro-, and trifluoromethyl groups was explained. The effect of substituents in the thienyl group on the stability of the magnesium haloalkoxycarbinolates was studied.     

The constitution of the grignard reagent : VIII. The structure of complexes between ethylmagnesium bromide and 1-ethoxy-2-methylbutane

From measurements of the degree of association and of the optical rotation of solutions of ethylmagnesium bromide in (+)(S)-1-ethoxy-2-methylbutane [(+)-(S)-L] and benzene it is concluded that these solutions contain the species EtMgBr·2L (I), (EtMgBr)₂·3L (III) and (EtMgBr·L)₂ (II) which have molecular rotations [M]²⁵_D of 3.79°, 5.92° and 4.26° respectively. Equilibrium constants of 103 mole/l and 1.41 mole/l at 25° were calculated for the equilibria between these species.     

The structure of the grignard reagent : IX. The crystal structure of the dimeric ethylmagnesium bromide/diisopropyl ether complex

The structure of the dimeric ethylmagnesium bromide/diisopropyl ether complex [C₂H₅MgBr - O(i-C₃H₇)₂]₂ was studied with s ingle crystal X-ray diffraction techniques. Crystals are monoclinic with spacegroup P2₁/n and two dimers per unit cell of dimensions a 7.85(1), b 14.43(2), c 11,31(2) °A, β 100.3(1)^o The structure was refined to a final R-value of 0.073. The magnesium is four coordinate; dimers are formed through bridging bromine atoms. p]This result is briefly discussed in the context of factors governing complex formation of Grignard reagents.     

A mild and efficient procedure for alpha-bromination of ketones using N-bromosuccinimide catalysed by ammonium acetate

Cyclic ketones reacted with N-bromosuccinimide (NBS) catalysed by NH(4)OAc in Et(2)O at 25 degrees C to give the corresponding alpha-brominated ketones in good yields, while acyclic ketones were efficiently brominated in CCl(4) at 80 degrees C.     

Preparation of ketones by direct reaction of grignard reagents with acid chlorides in tetrahydrofuran

Grignard reagents react with acid chlorides in tetrahydrofuran at low temperature to produce ketones in excellent yields. The results reported here strongly indicate the importance of the solvent in Grignard reagent chemistry.