Intramolecular 1,3-dipolar additions in 4-O-allyl pyranoside 6-nitrones: An approach to chiral pyrano-pyrans and pyrano-oxepans

Asymmetric 1,3-Dipolar Cycloaddition Reactions

“…In addition to the above-described reactions a number of alkenylnitrones derived from sugar derivatives have been applied in intramolecular 1,3-DC reactions. [131][132][133][134][135][136][137][138][139][140][141][142][143][144][145][146] The reactions leading to bicyclo-[3.3.0] compounds will be described first. Bernet and Vasella were the first to perform extensive studies in this field.…”

“…In addition to the above-described reactions a number of alkenylnitrones derived from sugar derivatives have been applied in intramolecular 1,3-DC reactions. − The reactions leading to bicyclo[3.3.0] compounds will be described first. Bernet and Vasella were the first to perform extensive studies in this field. − Glucose derivative 102 was converted into the 5-alkenyl aldehyde 103 and upon treatment with methylhydroxylamine, the resulting nitrone underwent intramolecular 1,3-DC reaction to give 104 as the only diastereomer in good yields (Scheme ) …”

“…Carbohydrate-derived alkenylnitrones have been used in an alternative manner for the synthesis of oxepanes. − ,,, Shing et al found that upon treatment of the glucose-derived aldehyde 105 with methylhydroxylamine, the resulting nitrone reacted to give a mixture of the oxepane 107a and tetrahydropyrane 107b , as pure diastereomers (Scheme ). , In this case the transition state 106a , in which the alkene termini is attached to the nitrone carbon atom is preferred over transition state 106b and the desired oxepane 107a is obtained as the major product. However, the regioselectivity is strongly controlled by the configuration of the C-3 of the furanose ring.…”

1,3-Dipolar cycloaddition reactions of carbohydrate derived nitrones and oximes

“…In similar studies Collins et al 35 and Shing et al 36 Resubmitting the deacetylated cycloadducts to the reaction conditions for a further 56 hours did not alter the product mixture thus hinting at a kinetically controlled reaction. It was proposed that the tetrahydropyrans were formed via a chair transition-state conformation (Fig.…”

Chiral Carbocyclic Nucleosides from d-Glucose: Enantiodivergent Synthesis and One-Pot Entry of Dimethylamino Functionality in the Purine Rings

“…In the previous paper we described a simple procedure for the enantioselective synthesis of a seven-membered carbocyclic nucleoside analogue using readily accessible precursors from d -glucose through an intramolecular nitrone cycloaddition reaction (INC). In a more versatile endeavor toward the extension of this methodology for realizing the synthesis of both the pure enantiomers of a nucleoside analogue incorporating five- and seven-membered carbocyclic rings, we envisioned to achieve the goal through INC reaction , of appropriately designed enose−nitrones from d -glucose, having nitrone functionality at C-5 or C-1 with the olefin at C-3 (Figure ). The success of such a scheme, however, hinged upon the mode of the cycloaddition leading to the desired stereochemistry at the newly generated chiral center at the ring junction.…”