Medium‐Sized Rings versus Macrocycles through Rhodium‐Catalyzed Ring‐Expansion Reactions of Cyclic Acetals

Abstract

α-Diazo β-ketoesters and diketones react with cyclic acetals under Rh(II) catalysis to yield unprecedented polyoxygenated 8- and 9-membered rings in one pot. The reactions occur under mild conditions with yields up to 90%. A perfect regioselectivity is obtained, which can be rationalized through a mechanistic hypothesis that considers 1) the formation of an oxonium ylide, 2) its transformation into an unsaturated acyclic oxocarbenium electrophilic intermediate, and 3) an intramolecular nucleophilic attack in a direct application of Baldwin's rules.

One-Step Synthesis of Nitrogen-Containing Medium-Sized Rings via α-Imino Diazo Intermediates

“…10,11 It was then debatable whether a general medium-size ring synthesis could be achieved using Nsulfonyl-1,2,3-triazoles 1 and cyclic ethers; other reactants such as acetals being possibly better reactive partners for the formation of the 8-and 9-membered rings. 12 Care was first taken to reproduce the THF insertion reaction in the absence of benzonitrile. 7b A series of N-sulfonyltriazoles was prepared following a copper-catalyzed procedure.…”

Pd(OAc)2-Catalyzed Macrocyclization of 1,2-Diazonaphthoquinones with Cyclic Ethers

“…Thus formed, these carbenes are electrophilic and readily react with various nucleophilic Lewis bases to generate the corresponding ylides, which are widely used in organic synthesis . For example, oxonium ylides are formed via the reaction of these carbenes and cyclic ethers, and then Stevens-type rearrangement, polymerization,or macrocyclization − proceeds subsequently. In the presence of a Rh-catalyst, carbenes formed from relatively stable diazo compounds, such as 2-diazo-1,3-dicarbonyl compounds 1 , react with cyclic ethers followed by preferential macrocyclization via oxonium ylide 2 to give the large cyclic ethers 3 and 4 with more than two molecules incorporated (Scheme , Paths a and b). , Although there are few reports on the formation of medium-sized ring products 5 via the intramolecular cyclization of ylide 2 (Path c), recently, Rh-catalyzed cyclization of 2-diazo-1,3-dicarbonyl compounds 1 and five- or six-membered ring cyclic acetals was achieved, which was designed by [N]- endo - trig cyclization ([N] = 8 or 9)…”

“…Interestingly, while only the Rh catalysts were reported to be effective for the metal-catalyzed macrocyclization reaction of cyclic ethers and α-carbonylcarbenes, , they were not efficient for the cyclization of 6a and THF (Table , entries 9–11).…”

Twin Polymerization: A Unique and Efficient Tool for Supporting Silver Nanoparticles on Highly Porous Carbon and Silica

“…Those are in line with the reported result for unsubstituted THP reacting with ethyl α‐diazoacetoacetate (31%) 9,10. Analogous derivatives 1d , 1e and 1f (X=Ph, CO 2 Me, OTBS) performed equally well or better since products 3d , 3e and 3f were obtained in 42 to 60% yields 11. A rather large variety of groups are thus compatible, in particular the nucleofugal ones that are not easily tolerated under Williamson ether synthesis conditions.…”