134692-46-9Relevant academic research and scientific papers
Reaction of γ-hydroy-N-[1-(dimethylcarbamoyl)ethyl]butanamides under the 'direct amide cyclization' conditions
Iliev, Boyan,Linden, Anthony,Heimgartner, Heinz
, p. 153 - 175 (2007/10/03)
The preparation of the title compounds was achieved via the 'azirine/oxazolone method' starting from the corresponding γ-hydroxy acids. Upon subjecting the γ-hydroxy-N-[1-(dimethylcarbamoyl)-ethyl] butanamides 4 to the so-called 'direct amide cyclization' (DAC) conditions, chlorinated acids 11 or imino lactones 12 were obtained as the sole products instead of the expected cyclodepsipeptides A or their cyclodimers (Scheme 4). Variation of the substituents in 4 did not affect the outcome of the reaction and a mechanism for the formation of both products from the intermediate oxazolone 13 has been proposed. Under the acidic conditions of the DAC, the imino lactones are formed as their HCl salts 12, which, in polar solvents or on silica gel, reacted further to give the chlorinated acids 11. Stabilization of the imino lactones was achieved by increasing the substitution in the five-membered ring, and their structure, in the form of the hydrochlorides, was established independently by X-ray crystallography (Fig. 4). A derivative 15 of the imino lactone 12a was prepared by the reaction with the 2H-azirin-3-amine 10a; its structure was also established by an X-ray crystal-structure determination (Fig. 3). Furthermore, the structures of the ω-chloro acids 11a and 11b were determined by X-ray crystallography (Fig. 2).
Cobalt(II) Chloride Catalyzed Acylation of Alcohols with Acetic Anhydride: Scope and Mechanism
Iqbal, Javed,Srivastava, Rajiv Ranjan
, p. 2001 - 2007 (2007/10/02)
Cobalt(II) chloride catalyzes the acetylation of a variety of alcohols with acetic anhydride in excellent yield.Primary hydroxyl groups can be selectively acylated in the presence of secondary and tertiary ones while the secondary hydroxyl groups can be preferentially acetylated in the presence of tertiary ones.Tertiary alcohols have been found to give ketones, acetoacetates, olefins, and diketene in addition to the acetate.The β-hydroxy esters and ketones can be acylated under these conditions without any elimination, and this reaction has been compared with 4-(dimethylamino)pyridine (DMAP)-mediated acylations where elimination of the resulting β-acetoxy carbonyl compound is observed.A detailed investigation of the acylation of tertiary alcohols has revealed that these reactions proceed via a tertiary alkoxy radical and ketene.A mechanism for these acylations is proposed by invoking an electron-transfer process.
Cobalt(II)chloride catalysed cleavage of ethers with acyl halides: Scope and mechanism
Iqbal,Srivastava
, p. 3155 - 3170 (2007/10/02)
Cobalt(II) chloride in acetonitrile catalyses the cleavage of a wide variety of ethers with acyl halides under mild conditions to give the corresponding esters in good yields. Acyclic aliphatic ethers are cleaved to the corresponding ester and chlorides whereas the cyclic aliphatic ethers give rise to the ω-chloroesters. The benzyl ethers can be converted to the corresponding esters along with the formation of benzyl chloride and benzyl acetamide. A comparative study for the cleavage of allyl and benzyl ether has revealed that benzyl ether can be selectively cleaved in presence of the allyl ethers. The oxiranes can be cleaved in highly regioselective manner to the corresponding-β-chloroesters. The vinyl ethers undergo sp2-hybridised carbon-oxygen bond cleavage under these conditions. Based on product analysis, a mechanism involving electron transfer followed by O-acylation and S(N)1 or S(N)2 attack by chloride-ion is discussed.
