Rapid stereocontrolled assembly of the fully substituted C-aryl glycoside of kendomycin with a Prins cyclization: a formal synthesis

Direct synthesis of tetrahydropyran-4-ones via O3ReOH-catalyzed Prins cyclization of 3-chlorohomoallylic alcohols

A new variation of Prins cyclization to directly and stereoselectively synthesize cis-2,6-disubstituted tetrahydropyran-4-ones from 3-chlorohomoallylic alcohols and aldehydes catalyzed by perrhenic acid is reported. The reaction is generally compatible with a range of aliphatic and aromatic aldehydes and 24 examples of tetrahydropyran-4-one products have been prepared in moderate to good yields. This methodology highlights the use of simple starting materials and commercially available aqueous perrhenic acid as a catalyst for Prins cyclization reactions to directly synthesize 2,6-disubstituted tetrahydropyran-4-ones.

Stereoselective Synthesis of Highly Substituted Tetrahydropyrans through an Evans Aldol-Prins Strategy

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 of the Evans aldol addition and the Prins cyclization allowed the diastereoselective and efficient generation of the desired oxacycles in two fashions: a one-pot Evans aldol-Prins protocol, in which five new σ bonds and five contiguous stereocenters were straightforwardly generated, and a two-step version, which additionally permitted the isolation of β,γ-unsaturated alcohol precursors bearing an N-acyl oxazolidin-2-one in the α position. From these alcohols were also obtained halogenated pentasubstituted tetrahydropyrans as well as 2,3,4,5-tetrasubstituted tetrahydrofurans, shedding light on the mechanism of the process. Computational studies were consistent with the experimental findings, and this innovative Evans aldol-Prins strategy was performed for the preparation of a battery of more than 30 densely substituted tetrahydropyrans, unprecedentedly fused to a 1,3-oxazinane-2,4-dione ring, both in a racemic fashion and in an enantiomeric fashion. These novel molecules were successfully submitted to several transformations to permit simple access to a variety of differently functionalized tetrahydropyrans. Most of these unique molecules were evaluated for their antimicrobial activity against Gram-positive and Gram-negative bacteria and the yeast Candida albicans, and some structure-activity relationships were established.

Three-Component, Diastereoselective Prins-Ritter Reaction for cis-Fused 4-Amidotetrahydropyrans toward a Precursor for Possible Neuronal Receptor Ligands

Here, we report an unprecedented, highly diastereoselective Prins-Ritter reaction of aldehydes, homoallylic alcohols, and nitriles in a three-component coupling reaction for the synthesis of tetra-cis-substituted 4-amidotetrahydropyrans. In this study, the reaction was not only applied for carbohydrate-based heterobicycles but also for more complex heterotricycles, showing acceptable levels of conversion yield (42-97% BRSM) and exclusive diastereoselectivity. Furthermore, the latter heterotricycles were converted to nine analogues of our neuronal receptor ligands IKM-159 and MC-27. An in vivo assay by intracerebroventricular injection in mice suggested that the substituent at C9 of the novel analogues interferes with the molecular interactions with the AMPA receptor, which was originally observed in the complex of IKM-159 and the GluA2 ligand binding domain. Our research has thus shown the power of a multicomponent coupling reaction for the preparation of a structurally diverse compound collection to study structure-activity relationships of biologically active small molecules.

The Evans Aldol–Prins cyclization: a general and stereoselective method for the synthesis of 2,3,4,5,6-pentasubstituted tetrahydropyrans

A method for the synthesis of 2,3,4,5,6-pentasubstituted THPs with good yields and diastereoselectivities through an Evans Aldol–Prins strategy is described.

A novel Prins cascade process for the stereoselective synthesis of oxa-bicycles

E- and Z-9-Methyldeca-3,8-dien-1-ols undergo smooth cyclization with aldehydes in the presence of 20 mol% AgSbF6 under extremely mild conditions to generate the corresponding oxa-bicycles in good yields with excellent selectivity. In fact, E-olefin affords the trans-product exclusively, whereas the Z-olefin gives the cis-product predominantly. In the case of E- or Z-8-methylnona-3,8-dien-1-ol, the product is formed via the termination of Prins cyclization with an allylic C-H bond through olefin migration. The termination of Prins cyclization with tethered olefin is an unprecedented reaction, which provides a useful motif of various natural products.

Highly (E)-selective BF(3).Et(2)O-promoted allylboration of chiral nonracemic alpha-substituted allylboronates and analysis of the origin of stereocontrol

Delta-methyl-substituted homoallylic alcohols 2 were prepared in 71-88% yield, E:Z >30:1 and 93% to >95% ee via BF(3).Et(2)O-promoted allylboration with alpha-Me-allylboronate 1. The origin of high (E)-selectivity is proposed.

Cerium(IV) sulfate catalyzed one-pot three-component diastereo selective synthesis of 4-amidotetrahydropyrans

A convenient and diastereoselective one-pot synthesis of cis-4-amidotetrahydropyrans is described. This simple protocol involves Prins cyclization of homoallylic alcohol and aldehydes, followed by Ritter reaction of acetonitrile leading to the formation of cis-4-acetamidopyrans in good yields.

Formal synthesis of (-)-kendomycin featuring a Prins-cyclization to construct the macrocycle

The kendomycin skeleton was prepared by a highly convergent strategy in which the benzofuran fragment and the acyclic iodide fragment were prepared by standard methods and joined using a Suzuki coupling. The distinctive reaction in our approach was an intramolecular Prins cyclization that assembles the macrocyclic ring in good yield. Modeling studies demonstrate that the acyclic chain is predisposed for macrocycle formation. Ultimately, the product was correlated with one of Lee's advanced intermediates for a formal total synthesis of kendomycin.

Rhenium(VII) catalysis of Prins cyclization reactions

The rhenium(VII) complex O3ReOSiPh3 is a particularly effective catalyst for Prins cyclizations using aromatic and alpha,beta-unsaturated aldehydes. The reaction conditions are mild, and the highly substituted 4-hydroxytetrahydropyran products are formed stereoselectively. Rhenium(VII) complexes appear to spontaneously form esters with alcohols and to directly activate electron-rich alcohols for solvolysis. Re2O7 and perrhenic acid are equally effective in catalyzing these cyclizations.

Total synthesis of (-)-kendomycin

An enantioselective synthesis of (-)-kendomycin is described and is based on the application of the organosilane-based [4 + 2]-annulation strategy for the assembly of the C1a-C10 fragment. An underutilized samarium(II) iodide-assisted cyclization (intramolecular Barbier-type reaction) is employed to afford the protected macrocycle.

A highly enantio- and diastereoselective 1,3-dimethylallylation of aldehydes

A highly enantio- and diastereoselective pentenylation of aldehydes is described. The homoallylic alcohol derived from 1,3-dimethylallylation of (-)-menthone undergoes an efficient allyl-transfer reaction with a wide range of aliphatic aldehydes in the presence of an acid catalyst to give rise to the corresponding 4-methyl-2(E)-penten-4-yl-5-ol products in good yields with high enantio- and 4,5-syn-selectivities.

Racemization in Prins cyclization reactions

Isotopic labeling experiments were performed to elucidate a new mechanism for racemization in Prins cyclization reactions. The loss in optical activity for these reactions was shown to occur by 2-oxonia-Cope rearrangements by way of a (Z)-oxocarbenium ion intermediate. Reaction conditions such as solvent, temperature, and the nucleophile employed played a critical role in whether an erosion in enantiomeric excess was observed. Additionally, certain structural features of Prins cyclization precursors were also shown to be important for preserving optical purity in these reactions.