The Role of the Sulfinyl Group on the Course of the Reactions of 3-p-Tolylsulfinylfuran-2(5H)-ones with Nitrones. Synthetic Uses of Cycloreversion Processes

Abstract

[reaction: see text] The reaction of enantiopure 3-p-tolylsulfinylfuran-2(5H)-ones (2a and 2b) with cyclic (4) and acyclic (6) nitrones afforded furoisoxazolidines (5 and 7) in high yields under mild conditions. The reactivity of the dipolarophile was dramatically enhanced by the sulfinyl group, which modulated the pi-facial selectivity (it was complete for reactions from 2b, yielding only the anti adducts) and was the main controller of the endo/exo selectivity. Cycloreversion processes from the resulting sulfinyl furoisoxazolidines proceeded readily and were to be considered to account for an improvement in the selectivity (facial and endo/exo) and even for an inversion of it when the composition of the reaction mixtures obtained under kinetic and thermodynamic conditions were quite different.

Synthesis of Maremycins A and D1 via Cycloaddition of a Nitrone with (E)-3-Ethylidene-1-methylindolin-2-one

“…Thus, reaction of nitrone 10 with 9 at −25 °C afforded a 47:53 mixture of 12 and 13 (entry 1), whereas reaction at 60 °C gave a 22:78 mixture (entry 3). Since a kinetically controlled reaction should exhibit a higher ratio at lower temperature, these results imply that the present cycloaddition at high temperature might involve a thermodynamically controlled equilibium cycloreversion of the cycloadducts 12 and 13 to the starting 9 and 10 . The effect of solvent polarity was next examined.…”

Isoxazolidine: A Privileged Scaffold for Organic and Medicinal Chemistry

“…However, LiAlH 4 in THF efficiently opened the isoxazolidine ring. Indeed, García Ruano et al performed the ring opening of isoxazolidine 180 at the same time as other transformations (lactone opening, alcohol deprotection, ester reduction) (Scheme ). However, LiAlH 4 being a potent reducing reagent that can affect several functional groups should be used with caution.…”

1,3-Dipolar Cycloadditions of Diazoalkanes to Activated Sulfoxides: Influence of Lewis Acids

“…Several years ago we initiated a program to explore the applicability of vinyl sulfoxides in asymmetric 1,3-dipolar reactions. In this context we have investigated the reactions with nitrile oxides, azomethine ylides, nitrones, and diazoalkanes. − In the last field we have reported excellent results from the two epimers at C-5 of 5-ethoxy-3- p -tolylsulfinylfuran-2(5 H )-ones 7 ( 1 in Scheme ), which evolved into adducts 2 in a highly stereoselective way and very good yields. Similar results were obtained in reactions of diazoalkanes with 3-sulfinylacrylonitriles 8 and 5-menthyloxy-4-phenylsulfinylfuran-2(5 H )-one .…”