25022-99-5Relevant academic research and scientific papers
Mild, Rapid, and Chemoselective Procedure for the Introduction of the 9-Phenyl-9-fluorenyl Protecting Group into Amines, Acids, Alcohols, Sulfonamides, Amides, and Thiols
Soley, Jacob,Taylor, Scott D.
, (2020/02/04)
The 9-phenyl-9-fluorenyl (PhF) group has been used as an Nα protecting group of amino acids and their derivatives mainly as a result of its ability to prevent racemization. However, installing this group using the standard protocol, which employs 9-bromo-9-phenylfluorene/K3PO4/Pb(NO3)2, often takes days and yields can be variable. Here, we demonstrate that the PhF group can be introduced into the amino group of Weinreb's amides and methyl esters of amino acids, as well as into alcohols and carboxylic acids, rapidly and in excellent yields, using 9-chloro-9-phenylfluorene (PhFCl)/N-methylmorpholine (NMM)/AgNO3. Nα-PhF-protected amino acids can be prepared from unprotected α-amino acids, rapidly and often in near quantitative yields, by treatment with N,O-bis(trimethylsilyl)acetamide (BSA) and then PhFCl/NMM/AgNO3. Primary alcohols can be protected with the PhF group in the presence of secondary alcohols in moderate yield. Using PhFCl/AgNO3, a primary alcohol can be protected in good yield in the presence of a primary ammonium salt or a carboxylic acid. Primary sulfonamides and amides can be protected in moderate to good yields using phenylfluorenyl alcohol (PhFOH)/BF3·OEt2/K3PO4, while thiols can be protected in good to excellent yield using PhFOH/BF3·OEt2 even in the presence of a carboxylic acid or primary ammonium group.
The Reaction between Acyl Halides and Alcohols: Alkyl Halide vs. Ester Formation
Strazzolini, Paolo,Giumanini, Angelo G.,Verardo, Giancarlo
, p. 217 - 254 (2007/10/02)
In the reaction between an acyl halide and an alcohol the thermodynamically favoured products are the free carboxylic acid and the alkyl halide.The initial reaction is, generally, the formation of an ester and HHal.When the alcohol is very prone to yield an alkyl cation upon protonation by HHal, formed H2O exhibited a superior reactivity and competed successfully with the alcohol for the acyl halide making, therefore, ester formation practically confined to a triggering role.But, in those cases where the cation is less easily formed, ester formation was favoured and, consequently, became the necessary elementary step towards alkyl halide formation.Tis final product, on the other hand, might be extremely slow to form in an SN2 reaction between the protonated ester function and the halide ion.In these instances, therefore, as well as in the cases when a basic solvent competes for the proton of HHal, the ester is the final product.A notable exception of the situation above outlined, is given by α-hydroxy-α-phenylbenzeneacetic acid (2y), which appears to undergo direct chlorine-hydroxyl interchange through a quaternary intermediate (E), in the end collapsing to α-chloro-α-phenyl-benzeneacetic acid (4y).Different systems were compared using CH2Cl2 as a solvent under strictly similar conditions.Some 28 different substrates were tested for reaction with AcCl (1a), whereas the action of eight acyl halides (a) against (RS)-α-methylbenzenemethanol (2n) and α-phenylbenzenemethanol (2p), as well as the effect of five different solvents on the reaction between two alcohols (2p and 2-methyl-2-propanol, 2c) with 1a, were observed.
Versatile and Convenient Lattice Hosts derived from Singly Bridged Triarylmethane Frameworks, X-Ray Crystal Structures of Three Inclusion Compounds
Weber, Edwin,Doerpinghaus, Norbert,Csoeregh, Ingeborg
, p. 2167 - 2177 (2007/10/02)
A new family of host molecules, based on the singly bridged triarylmethanol and triarylacetic acid frameworks, is described.These hosts form crystalline inclusions with a variety of uncharged organic molecules ranging from protic dipolar to apolar compounds (130 different species).The formation and stoicheiometry depend in a systematic manner on structural parameters of the host, such as the nature of the functional group and the substituents, and on the substituent positions.The crystal structures of three inclusion compounds have been studied by X-ray diffraction.They reveal the building principles of the new inclusion family.In the crystals of 1a*benzene (8:3), the benzene is interstitially entrapped by H-bonded tetramer clusters of 1a.Crystals of 1a*dioxane (4:3) are built of H-bonded 2:1 host-guest complexes including interstitial molecules of dioxane.In the case of 4c*EtOH (1:1), the building principle is formation of 2:2 host-guest clusters via a twelve-membered H-bonded ring.
