Stereocontrolled Preparation of Spirocyclic Ethers by Intramolecular Trapping of Oxonium Ions with Allylsilanes

Paquette, Leo A.; Tae, Jinsung

doi:10.1021/jo961306k

Cited by 34 publications

(11 citation statements)

References 38 publications

(20 reference statements)

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“…Although the PC of exocyclic oxocarbenium ions had been widely employed in the synthesis of spiroethers,24 examples of PC of endocyclic oxocarbenium ions have not, to the best of our knowledge, been described 3,24. However, the synthesis of spiroethers through Sakurai cyclization of endocyclic oxocarbenium ions had been studied 5a,25,26…”

Section: Resultsmentioning

confidence: 99%

“…The energetically favored TS TS‐ XXVII eq α is attained on starting from the 5,6‐diequatorial conformer XXVII eq . It features 1) an anti ‐addition of Nu – along a pseudoaxial trajectory, 2) a half‐chair‐like conformation,25,40,41c and 3) a syn ‐1,3‐diaxial arrangement of Nu and 6‐H, and it yields XXVIII . The alternative TS TS‐ XXVII ax β , which has basic features similar to those of TS‐ XXVII eq α but has R 1 in a pseudoaxial position, gives the minor diastereomer XXIX and is kinetically disfavored because of 1,3‐diaxial strain 37.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Spiro‐ and Bicycloannulation of Sulfoximine‐Substituted 2‐Hydroxy‐dihydropyrans: Enantioselective Synthesis of Spiroketals, Spiroethers, and Oxabicycles and Structure of Dihydropyran Oxocarbenium Ions

et al. 2013

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A modular enantioselective synthesis of spiroketals, spiroethers, and oxabicycles, each containing a dihydropyran subunit, is described. It is based on the 2,2‐spiro‐ and 2,6‐bicycloannulation of sulfoximine‐substituted 2‐hydroxy‐dihydropyrans. Key steps of the spiroannulations are the ring‐closing metathesis of the corresponding 2,2‐oxadienyl and 2,6‐dienyl dihydropyrans and Prins cyclization of 2‐alkenyl 2‐hydroxy‐dihydropyrans. Ring‐closing metathesis of the corresponding 2,6‐dienyl dihydropyrans gave oxabicycles with oxabicyclo[4.3.1]decane skeletons. These routes were extended to the synthesis of spiroketals and spiroethers incorporating additional annulated six‐membered rings. Diastereoselective Prins cyclization of mono‐ and bicyclic 2‐alkenyl‐2‐hydroxy‐dihydropyrans was highly selective and afforded chloro‐substituted spirocycles. Substituted 2‐hydroxy‐dihydropyrans were obtained through cyclization of δ‐hydroxy ketones, which were synthesized from enantiomerically pure sulfoximine‐substituted homoallylic alcohols through lithiation and trapping of the α‐lithioalkenylsulfoximines with unsaturated aldehydes, followed by allylic oxidation. Inter‐ and intramolecular glycosidations of the 2‐hydroxy‐dihydropyrans with O‐ and C‐nucleophiles proceeded with high stereoselectivities and furnished 2,6‐trans‐configured glycosides. Dihydropyran oxocarbenium ions are most likely intermediates in the glycosidations. According to ab initio calculations, sulfoximine‐ and trimethyl‐substituted dihydropyran oxocarbenium ions adopt a half‐chair‐like conformation. The energy difference between the oxocarbenium ion with pseudoaxial and the one with pseudoequatorial methyl groups is very small. A transition state model for their reactions with nucleophiles is proposed. It features a half‐chair‐like conformation, a pseudoequatorial C6 substituent, and an anti‐addition of the nucleophile along an axial trajectory to C2 that produces an anti‐periplanar lone pair at the O atom. A similar transition state model allows a general explanation for the trans stereoselectivity of the reactions between C6‐substituted dihydropyran oxocarbenium ions and nucleophiles.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Spiro‐ and Bicycloannulation of Sulfoximine‐Substituted 2‐Hydroxy‐dihydropyrans: Enantioselective Synthesis of Spiroketals, Spiroethers, and Oxabicycles and Structure of Dihydropyran Oxocarbenium Ions

et al. 2013

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“…Gais and co‐workers synthesized enantiopure spiroethers from α‐hydroxydihydropyrans by Prins cyclization . Although spiroethers had been achieved through Prins cyclization already, intramolecular trapping of a dihydropyranyl cation leading to a spiroether bearing a Cl atom on the carbocyclic ring was a new variant , .…”

Section: Spiro Cyclization: Monocyclizationmentioning

confidence: 99%

Recent Advances in Prins Spirocyclization

et al. 2017

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The classical Prins cyclization has been one of the most intensively studied reactions during the last two decades, and it has found many applications in key steps of natural product syntheses, especially for products containing tetrahydropyran motifs and related structures in their core skeletons. The application of this reaction to the synthesis of spirocylic networks has made substantial progress recently. Spiro motifs are found in many natural products with promising biorelevance and are increasingly being incorporated in drug candidates. Further, various spirocyclic chiral ligands have shown promising efficiency in asymmetric synthesis. Here a compilation of recent spiroannulation reactions by Prins cyclization is presented, focusing on the scope and versatility of this method.

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“…Spiro-fused tetrahydropyran and furan ring systems have been prepared by spiroether formation [27] intramolecular radical addition [28], and intramolecular reaction of an oxonium ion with an allyl silane [29]. More recently ring closing metathesis was applied to carbohydrates for the construction of highly functionalised carbohydrate-based structures [30].…”

Section: Polycyclic Glycidic Scaffoldsmentioning

confidence: 99%