[reaction: see text] A new iron(III) halide-promoted aza-Prins cyclization between gamma,delta-unsaturated tosylamines and aldehydes provides six-membered azacycles in good to excellent yields. The process is based on the consecutive generation of gamma-unsaturated-iminium ion further nucleophilic attack by unsaturated carbon-carbon bond. Homoallyl tosylamine leads trans-2-alkyl-4-halo-1-tosylpiperidine as major isomer. In addition, alkyne homopropargyl gives...

Iron(III) halides have proven to be excellent catalysts in the coupling of acetylenes and aldehydes. When terminal were used main products obtained 1,5-dihalo-1,4-dienes with (E,Z)-stereochemistry contaminated some cases (E)-alpha,beta-unsaturated ketones. The former carbonyl derivatives sole isolated when nonterminal aromatic alkynes used. homopropargylic alcohols used, a Prins-type cyclization occurred yielding 2-alkyl-4-halo-5,6-dihydro-2H-pyrans. In addition, anhydrous ferric are also...

[reaction: see text] A new type of Prins cyclization using silylated secondary homopropargylic alcohols and aldehydes yielding tetra- pentasubstituted dihydropyrans is described. The presence the trimethylsilyl group in triple bond favors minimizes 2-oxonia-[3,3]-sigmatropic rearrangement as a competitive alternative pathway. Ab initio theoretical calculations species involved rearrangements support proposed mechanism. process highly stereoselective, affording cis-dihydropyran only isomer.

A systematic approach to the enantiomeric synthesis of all possible diastereoisomers 2,6-dialkyl-3,5-dioxytetrahydropyrans is described. The key step in described methodology intramolecular cyclization enantiomerically enriched (≥95% ee) 7-hydroxy-4-(benzoyloxy)-2,3-unsaturated esters. In fused systems, six eight for one series were synthesized using this procedure as a step. Using those with suitable stereochemistry, two left by simple chemical transformations: case basic isomerization...

Prins cyclization of bis-homoallylic alcohols with aldehydes catalyzed by iron(III) salts shows excellent cis selectivity and yields to form 2,7-disubstituted oxepanes. The is able catalyze this process unactivated olefins. This was used as the key step in shortest total synthesis (+)-isolaurepan.

An efficient alkene aza-Cope−Mannich cyclization between 2-hydroxy homoallyl tosylamine and aldehydes in the presence of iron(III) salts to obtain 3-alkyl-1-tosyl pyrrolidines good yields is described. The process based on consecutive generation a γ-unsaturated iminium ion, 2-azonia-[3,3]-sigmatropic rearrangement, further intramolecular Mannich reaction. Iron(III) are also shown be excellent catalysts for new using homopropargyl tosylamine.

The relative stability of the intermediates involved in alkyne Prins cyclization and competitive 2-oxonia-[3,3]-sigmatropic rearrangement was studied. This shown to occur slowly under typical conditions when allenyl oxocarbenium ion that results from is similar or higher energy than starting alkynyl ion. formal may be disfavored by destabilizing resultant stabilizing an intermediate dihydropyranyl cation. trimethylsilyl group as a substituent at electron-withdrawing groups (CH2Cl CH2CN)...

A highly efficient, diastereoselective, iron(III)-catalyzed intramolecular hydroamination/cyclization reaction involving α-substituted amino alkenes is described. Thus, enantiopure trans-2,5-disubstituted pyrrolidines and trans-5-substituted proline derivatives were synthesized by means of a combination starting materials, easily available from l-α-amino acids, with sustainable metal catalysts such as iron(III) salts. The scope this methodology highlighted in an enantiodivergent approach to...

A computational study at the ab initio level of cyclization (E)- and (Z)-7-hydroxy-4-substituted-2,3-unsaturated esters leading to 2,3-disubstituted tetrahydropyrans has been performed. The showed requirement coordination between pre-tetrahydropyranyl oxygen that carbonyl α,β-unsaturated ester with cation base used obtain a suitable transition state model. calculations using 6-31G*//3-21G basis set show different relative stabilities for final products states them. 6-31+G* was as calibration...

A mild and new procedure for the selective cleavage of an alkoxycarbonyl group (Boc, CBz) in N,N-dicarbamoyl-protected amino compounds is described. The method based on use lithium bromide acetonitrile compatible with a large range other functionalities present substrates. Compared reported methodologies, particularly useful Cbz-selective N,N-Ts,Cbz-diprotected amines. rationalization selectivity supported by ab initio calculations also presented.

A selective, catalytic and practical method for removing a Boc group from several <italic>N</italic>,<italic>N</italic>′-diprotected amino acids amine derivatives using iron(<sc>iii</sc>) salts as sustainable catalysts is described.

Ambiphilic allenes are generated by an organocatalyzed domino reaction of alkyl propiolates and aromatic 1,2-diketones; in the absence any external chemical agent, these perform a thermally-driven dimerization to generate corresponding fully-substituted cyclobutanes regio- highly stereoselective manner.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStereoselective Synthesis of Highly Substituted .gamma.-Lactones and Butenolides by Intramolecular Michael Addition Enantiomerically Enriched .gamma.-[(Phenylthio)acyl]oxy .alpha.,.beta.-Unsaturated EstersCarmen M. Rodriguez, Tomas Martin, Miguel A. Ramirez, Victor S. MartinCite this: J. Org. Chem. 1994, 59, 16, 4461–4472Publication Date (Print):August 1, 1994Publication History Published online1 May 2002Published inissue 1 August...

A direct and general method for the synthesis of naturally occurring 2,3,4,5,6-pentasubstituted tetrahydropyrans has been developed, employing β,γ-unsaturated N-acyl oxazolidin-2-ones as key starting materials. The combination Evans aldol addition Prins cyclization allowed diastereoselective efficient generation desired oxacycles in two fashions: a one-pot aldol–Prins protocol, which five new σ bonds contiguous stereocenters were straightforwardly generated, two-step version, additionally...

The intramolecular Nicholas reaction of propargylic alcohols derived from N,N-acyl-diprotected ω-semialdehydes obtained glutamic acid provided stereoselectively 5-alkynylproline derivatives. suitable choice the N-protecting group (tosyl or benzoyl derivative) permitted control stereochemistry during ring formation. Semiempirical calculations species involved in cyclization support observed stereochemistry.

A highly regio- and stereoselective intramolecular [1,5]-hydrogen-transfer process is described. Treatment of gamma-benzyl-protected Co2(CO)6-alpha,gamma-acetylenic diols with BF3 x OEt2 provides bis-homopropargylic alcohols. The reaction occurs within seconds, tolerates a wide range functionalities, good yields. When the ether group located at stereochemically defined carbon atom, rearrangement high stereoselectivity, transferring chirality carbinol center to newly created stereocenter....

The scope and limitations of an expeditious synthesis substituted butenolides from 3-substituted or 3,4-disubstituted furans is described. entire process embodies a controlled oxidation the furan core to 2,5-dialkoxy-dihydrofuran intermediate regioselective acid-catalyzed hydrolysis butenolide ­derivative. 3-Substituted yield exclusively 2-substituted butenolides. Calculations studies provide substantiation proposed mechanism.