Grignard reagents ethynyl

Generally, in contrast to 2-substituted cyclopentanones, the diastereoselectivity of addition reactions to 3-substituted cyclopentanones is nearly independent of the nucleophile and the substituent in the 3-position. Thus, addition of various Grignard reagents, including ethynyl reagents, to 3-methyl- and 3-ferf-butylcyclopentanone leads to almost the same ratio of diastereomers (Table 3)3,4 6, 27,2s... 

The reaction of 4-(phenylsulfonyl)azetidin-2-one (128) with nucleophiles such as dialkylcopper lithium and Grignard reagents gives 4-alkyl, 4-allyl, 4-vinyl or 4-ethynyl-azetidinon-2-one (129) in good yields (equation 99)83. The yields of several azetidin-2-ones obtained by this method are given in Table 10. The reaction apparently proceeds through an intermediate azetin-2-one 131 derived from the five-membered coordination complex (equation 100). 

Adition of Grignard reagents. Reaction of 2,3-O-isopropylidene-D-ribose (62) with ethynyl magnesium bromide gives l,2-dideoxy-4,5-0-iso-propylidene-D-a//o-hept-l-ynitol (63), which is then converted into its 7-O-trityl ether (64). Treatment of 64 with TsCl/pyridine provides 2,3-0-isopropylidene-5-0-trityl-a-D-ribofuranosylethyne (65) which upon deprotection affords derivative 66 (Scheme 22).89... 

Ethynyl-/3-propiolactone (75) reacts regioselectively with Grignard reagents in the presence of the Cul catalyst to afford 3,4-alkadienoic acids 76 in high yields (Scheme 3.38) [84],... 

In an investigation of the stereoselectivity of nucleophilic addition to larger ring systems, ethyl-, vinyl-, and ethynyl-lithium and -Grignard reagents have been added to 2-(3 -phenylpropyl)cycloheptanone (69). In all cases, the predominant product is the cw-alcohol, and calculations have been used to identify the steric and torsional effects in the transition state that favour this stereochemistry. 

Nucleophilic additions of ethyl-, vinyl-, and ethynyl-lithium and Grignard reagents to a 2-alkyl-substituted cycloheptanone have been found to yield the corresponding cw-cycloheptanol preferentially. The selectivity, which increases with size of the nucleophile, has been attributed to a combination of steric repulsions and torsional effects in the transition state. Application of the MM2 force field to analyse nucleophilic attack of hydride and ethynyl lithium on 2-methylcycloheptanone gave results comparable to those obtained experimentally and from ab initio calculations. 

Owing to their stability and low nucleophilicity, metal acetylides are less reactive toward Cjq than other lithium organyls or Grignard reagents [11]. Though the reaction is slower and higher reaction temperatures are necessary, various acetylene derivatives of Cjq could be obtained. The first acetylene Cjq hybrids were (trimethyl-silyl)ethynyl- and phenylethynyl-dihydro[60]fullerene, synthesized simultaneously... 

Grignard reagents (equations 139 and 140).1218 Ethynyl complexes were also prepared according to equation (141).1218... 

Stereocontrolled ethynylation of methyl 2,3,4-tri-O-benzyl-a-D-g/Hco-hexodialdo-l,5-pyranoside (52) with a Grignard reagent formed from trimethylsilylacetylene, followed by a multistep procedure afforded the aminouronic acid 53, the a-amino acid on which miharamycin A is based.168 Uronic acid derivatives have also been produced by the Wittig reaction on the aldehydic side chain of dialdofuranose compounds.169... 

Thienylmagnesium or zinc derivatives can be coupled with vinyl halides, bromo- or iodobenzene, or ethynyl bromide under Ni or Pd catalysis (Scheme 148) a thien-2-yl Grignard reagent was coupled twice to 3,6-dibromocar-bazole using nickel catalysis <1997CM1578>. The reaction can be extended to the synthesis of -styrylthiophene in this case the double-bond configuration is retained in the product. 

The nucleophilic addition of an acetylide to form an ethynyl alcohol and the addition of organometallic reagents such as Grignard reagents to carbonyl compounds are important methods for C-C bond formation. 

Aryl tellurium halides react with aliphatic and aromatic Grignard reagents, with ethenyl magnesium halides , with ethynyl magnesium bromide with dimethyl and diethyl cadmium , with 2-(diphenylphosphino)-phenyl lithium, and with phenyl mercury chloride to produce aryl organo telluriums (p. 416). 

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