The fluorination of ketones, ketals, and enamides has been achieved using the electrophilic fluorinating reagent Selectfluor™ (F-TEDA-BF4). For the reactions of ketones and ketals the use of sulfuric acid (0.1equiv) as an additive was found to facilitate the reaction leading to more rapid product formation. This behavior is analogous to the known effects of acid catalysis on the bromination of ketones. The reactions were generally quite selective leading to the formation of monofluorinated products, and could be accomplished on reaction scales up to 85mmol using N-protected piperidone based substrates. Reactions in the presence of MeOH led to the formation of the corresponding fluoroketones or fluoroketals depending upon the substrate. The formation of the fluoroketals in this manner, as well as the fluorination of cyclic enamides are examples of multi-component coupling reactions.

A diastereoselective synthesis of fluoropiperidine quinazoline spirocycles has been developed through a silyl triflate mediated intermolecular coupling of difluorobenzamidine and racemic N-protected 3-fluoropiperidine dimethyl ketals or piperidones. Combination of the silyl reagents together with Lewis acids (such as BF3·OEt2, ZnCl2, InCl3, etc.) accelerated the coupling reaction to afford the desired fluorospirocycles in good yields (40–83%) and high diastereoselectivity. A ratio of the two diastereoisomers of up to 10:1 in favor of the desired isomer can be achieved.

AbstractA simple method is developed for the addition of Grignard reagents (in either Et2O or THF) to cyclic sulfamidate imines to give 4‐disubstituted derivatives.

The addition of Grignard reagents to cyclic sulfamidate imines has been developed as a facile method for the synthesis of N-substituted quaternary sulfamidates. By way of ring opening with an appropriate nucleophile, versatile synthons for 1,2-amino alcohols, 1,2-diamines, and beta-amino acids are produced.

Enantioselective palladium(II)-catalyzed formal [3,3]-sigmatropic rearrangement of (E)- and (Z)-allyloxy substituted N-heterocycles generates N-allyl N-heterocyclic amides in good yields and high enantioselectivities (up to 96% ee). The chiral palladacycle COP-Cl (5 mol %) is used as a catalyst with silver(I) trifluoroacetate (10 mol %) at 35-45 degrees C. Examples of heterocycles synthesized include 2-pyridones, quinolin-2(1H)-ones, and isoquinolin-1(2H)-ones.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

CO! You had me at hello: The use of chiral biphenyl-based phosphoramidite ligands on rhodium provides an efficient [2+2+2] cycloaddition between terminal alkyl alkynes and alkenyl isocyanates (see scheme). The cycloaddition proceeds through a CO migration pathway, and facilitates a rapid four-step asymmetric synthesis of indolizidine (-)-209D.

This manuscript describes the development and scope of the asymmetric rhodium-catalyzed [2 + 2 + 2] cycloaddition of terminal alkynes and alkenyl isocyanates leading to the formation of indolizidine and quinolizidine scaffolds. The use of phosphoramidite ligands proved crucial for avoiding competitive terminal alkyne dimerization. Both aliphatic and aromatic terminal alkynes participate well, with product selectivity a function of both the steric and electronic character of the alkyne. Manipulation of the phosphoramidite ligand leads to tuning of enantio- and product selectivity, with a complete turnover in product selectivity seen with aliphatic alkynes when moving from Taddol-based to biphenol-based phosphoramidites. Terminal and 1,1-disubstituted olefins are tolerated with nearly equal efficacy. Examination of a series of competition experiments in combination with analysis of reaction outcome shed considerable light on the operative catalytic cycle. Through a detailed study of a series of X-ray structures of rhodium(cod)chloride/phosphoramidite complexes, we have formulated a mechanistic hypothesis that rationalizes the observed product selectivity.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

A highly regioselective rhodium-catalyzed intermolecular [2+2+2] cycloaddition of terminal alkynes with a variety of isocyanates to provide 2- and 4-pyridones has been developed. This reaction proceeds in good to excellent yields and overcomes the problem of dimerization and trimerization through the use of phosphoramidite ligands. A CO migration in the metallacycle is proposed to account for the formation of 4-pyridone.

An enantioselective synthesis of indolizidines bearing quaternary substituted stereocenters by way of a rhodium-catalyzed [2 + 2 + 2] cycloaddition of substituted alkenyl isocyanates and terminal alkynes is described. The reaction provides lactam products using aliphatic alkynes, whereas aryl alkynes give rise to vinylogous amide products. Through modification of the phosphoramidite ligand, high levels of enantioselectivity, regioselectivity, and product selectivity are obtained for both products.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access the actual ChemInform Abstract, please click on HTML or PDF.

The synthesis of N-protected allylic amines has been achieved utilizing a palladium(II)-catalyzed, [3,3]-rearrangement of (allyloxy) iminodiazaphospholidines. This [3,3]-aza-phospha-oxa-Cope sigmatropic rearrangement reaction is thermodynamically driven by a P=N to P=O interconversion and is an alternative to the Overman rearrangement. The overall process involves the nucleophilic displacement of an allylic alcohol onto a P(III) precursor, followed by a Staudinger reaction to generate the (allyloxy) iminodiazaphospholidine precursors. Pd(II)-catalyzed [3,3]-aza-phospha-oxa-Cope rearrangement then gives a phosphoramide, which is readily hydrolyzed under acidic conditions to yield allylic amine derivatives. Pd(II) catalysis is believed to occur in a fashion analogous to that of the rearrangement of allylic imidates. The scope of racemic, diastereoselective, and enantioselective variants of this rearrangement is described. The use of chiral diamine auxiliaries in diastereoselective rearrangements is reported. Rearrangement of chiral N,N'-dimethyl cyclohexanediamine derived diazaphospholidines gives rise to phosphoramides with moderate diastereoselectivities (up to 3.5:1 dr). The same major diastereomeric product in these rearrangements was prepared irrespective of the starting allylic alcohol geometry. An enantioselective variant of the reaction was demonstrated for the rearrangement of cis-(allyloxy) iminodiazaphospholidines with cobalt oxazoline palladacycle (COP-X) catalysts (5 mol %) in high yield and enantioselectivity (up to 96% ee).

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A new selenoglycoside, phenyl 2,3,5,6-tetra-O-acetyl-4-thio-1-selenogalactofuranose, has been synthesized. This 4-thiogalactofuranosyl donor was used in the syntheses of heteroatom analogues of the di-, tri-, and tetrasaccharides corresponding to the oligosaccharide β-d-Galf-(1→3)-α-d-Manp-(1→2)-(β-d-Galf-(1→3))-α-d-Manp. These compounds represent fragments of the terminal end of the glycosylinositolphospholipid oligosaccharide found in the protozoan Trypanosoma cruzi, the causative agent of Chagas disease, and are intended for use as inhibitors of the enzymes that construct the native oligosaccharides. The syntheses employed the selective activation of a phenyl 4-thio-1-selenogalactofuranoside glycosyl donor over ethyl 1-thioglycoside glycosyl acceptors with NIS/TfOH.