Abstract:Nearly two decades of work on ring-contraction reactions is discussed in this account. We have developed several reliable protocols for the rearrangement of a number of different substrates using thallium(III) salts and, more recently, hypervalent iodine(III) reagents. A variety of ring systems, such as cyclopentanes, cis-and trans-hydrindanes, and indanes, can be obtained using these methods. Additionally, the stereoselective total syntheses of the sesquiterpenes (±)-, (-)-and (+)-mutisianthol and (+)-bakkeno… Show more
“…For N‐heterocycles used in this reaction, one N‐substituent must be benzhydryl, or both N‐substituents must bear stabilizing elements such as benzyl, allyl or be positioned α to a carbonyl group. Inspired by our previous work, [13, 16] herein we report a N‐atom deletion of N‐heterocycles via a sequence of N ‐sulfonylazidonation, Curtius‐type rearrangement and subsequent rearrangement of the 1,2‐diazene intermediate, providing a unique opportunity to promote ring contraction [17] of N‐heterocycles (Scheme 1 F).…”
Excising the nitrogen in secondary amines, and coupling the two residual fragments is a skeletal editing strategy that can be used to construct molecules with new skeletons, but which has been largely unexplored. Here we report a versatile method of N‐atom excision from N‐heterocycles. The process uses readily available N‐heterocycles as substrates, and proceeds by N‐sulfonylazidonation followed by the rearrangement of sulfamoyl azide intermediates, providing various cyclic products. Examples are provided of deletion of nitrogen from natural products, synthesis of chiral O‐heterocycles from commercially available chiral β‐amino alcohols, formal inert C−H functionalization through a sequence of N‐directed C−H functionalization and N‐atom deletion reactions in which the N‐atom can serve as a traceless directing group.
“…For N‐heterocycles used in this reaction, one N‐substituent must be benzhydryl, or both N‐substituents must bear stabilizing elements such as benzyl, allyl or be positioned α to a carbonyl group. Inspired by our previous work, [13, 16] herein we report a N‐atom deletion of N‐heterocycles via a sequence of N ‐sulfonylazidonation, Curtius‐type rearrangement and subsequent rearrangement of the 1,2‐diazene intermediate, providing a unique opportunity to promote ring contraction [17] of N‐heterocycles (Scheme 1 F).…”
Excising the nitrogen in secondary amines, and coupling the two residual fragments is a skeletal editing strategy that can be used to construct molecules with new skeletons, but which has been largely unexplored. Here we report a versatile method of N‐atom excision from N‐heterocycles. The process uses readily available N‐heterocycles as substrates, and proceeds by N‐sulfonylazidonation followed by the rearrangement of sulfamoyl azide intermediates, providing various cyclic products. Examples are provided of deletion of nitrogen from natural products, synthesis of chiral O‐heterocycles from commercially available chiral β‐amino alcohols, formal inert C−H functionalization through a sequence of N‐directed C−H functionalization and N‐atom deletion reactions in which the N‐atom can serve as a traceless directing group.
“…For Nheterocycles used in this reaction, one N-substituent must be benzhydryl, or both N-substituents must bear stabilizing elements such as benzyl, allyl or be positioned a to a carbonyl group. Inspired by our previous work, [13,16] herein we report a N-atom deletion of N-heterocycles via a sequence of Nsulfonylazidonation, Curtius-type rearrangement and subsequent rearrangement of the 1,2-diazene intermediate, providing a unique opportunity to promote ring contraction [17] of Nheterocycles (Scheme 1 F).…”
Excising the nitrogen in secondary amines, and coupling the two residual fragments is a skeletal editing strategy that can be used to construct molecules with new skeletons, but which has been largely unexplored. Here we report a versatile method of N‐atom excision from N‐heterocycles. The process uses readily available N‐heterocycles as substrates, and proceeds by N‐sulfonylazidonation followed by the rearrangement of sulfamoyl azide intermediates, providing various cyclic products. Examples are provided of deletion of nitrogen from natural products, synthesis of chiral O‐heterocycles from commercially available chiral β‐amino alcohols, formal inert C−H functionalization through a sequence of N‐directed C−H functionalization and N‐atom deletion reactions in which the N‐atom can serve as a traceless directing group.
“…One of them is the ring contraction of 1,2‐dihydronaphthalenes promoted by thallium(III) or by iodine(III). This oxidative rearrangement has the main feature to provide trans ‐1,3‐disubstituted indanes in a diastereoselective manner, constituting the key step in the chemical synthesis of (±)‐indatraline, as well as in the total synthesis of natural products, such as (+)‐mutisianthol, and (+)‐ trans ‐trikentrin (Scheme ) . A mechanism has been suggested to explain the diastereaselectivity of this transformation .…”
The metal‐free synthesis of the trans‐1,3‐disubstituted indanes through the ring contraction of 1,2‐dihydronaphtalenes, promoted by PhI(OH)Ts (HTIB or Koser's reagent), was computationally studied using Density Functional Theory (DFT) methods. DFT calculations suggest that the stereoselectivity of these reactions arises through the torsional effects during the electrophilic addition of the hypervalent iodine to the double bond of the 1,2‐dihydronaphthalene. Furthermore, the fundamental role played by the solvent (MeOH) during the nucleophilic addition step was analyzed by DFT methods on a mixed continuum‐microsolvation model system.
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