Notizen/Notes Kronenether aus o‐Chinondiaziden und Oxetan

Abstract

Crown Ethers from o‐Quinone Diazides and Oxetane The carbenes 11, generated by photolysis of the di‐ and tetrachloro‐o‐quinone diazides 10, react with oxetane in a 1:3 ratio to give the 15‐membered crown ethers 19. In the presence of methanol, the oxonium ions 12 are trapped with formation of 1‐(aryloxy)‐3‐methoxypropanes (13). In the absence of additional nucleophiles, 12 reacts with oxetane until the chain length is appropriate for inverting intramolecular attack of the aryl oxide at the α‐carbon atom of the oxonium ion (18 → 19).

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)…”

Macrocyclization of Oxetane Building Blocks with Diazocarbonyl Derivatives under Rhodium(II) Catalysis

“…These derivatives react readily in the presence of Brønsted or Lewis acids to promote polymerization reactions 6. Macrocyclizations, which, in principle, can be also afforded in these reactions, are rare 7. In this context, we report the unusual Rh II ‐catalyzed condensation of oxetanes 1 and α‐diazocarbonyls 2 that yields exclusively a rare type of functionalized 15‐membered macrocycle 3 [Eq.…”

“…Previously, it has been shown that macrocycles can be generated from oxonium ylides 8. These intermediates are readily prepared by reactions of ethers and α‐diazocarbonyls under photoirradiation, electrophilic activation, or metal catalysis 7. 9 For instance, 18‐membered macrocycles were recently prepared in a single step by the condensation of two α‐diazo‐β‐ketoesters and two cyclic ethers (1,4‐dioxane, tetrahydropyrane) in the presence of [Rh 2 (OAc) 4 ] or [Rh 2 (Oct) 4 ] 9d.…”

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

“…Simpler 7‐, 8‐, or 9‐membered rings of type 8 , 9 , and 10 [Eqs. (4), (5) and (6)], which could have resulted from intramolecular reactions of nucleophilic and electrophilic sites within ylides 5 , 6 , and 7 , were either not observed or appeared only in trace amounts 4a. 5 Herein, in a mechanistic exercise with synthetic applications, the macrocyclic reactivity is directed towards the exclusive formation of analogues of 8 , 9 , and 10 ; this was achieved through the direct application of Baldwin’s rules6 and a modification of the oxo‐nucleophiles.…”