Reaction of Vinylcarbenoids with Benzaldehydes:  Formation of Vinylcarbonyl Ylides Followed by Ring Closure to Oxiranes and Dihydrofurans

Abstract

Rh(2)(OAc)(4)-catalyzed reaction of vinyldiazo compound 1a in the presence of p-methoxybenz- 2a, mesit- 2b, and p-chlorobenzaldehyde 2c gave a mixture of isomeric vinyloxiranes 3a-c and 4a-c, and sterically unstable (E)-dihydrofurans 5a-c, but not stable (Z)-dihydrofurans 6. However, the reactions with p-nitro- 2d and 2,4-dinitrobenzaldehyde 2e gave (Z)-dihydrofurans 6d,e along with 3d, 4d, and 5d,e. The reaction in the presence of maleic anhydride and dimethyl fumarate gave single 1,3-dipolar cycloadducts 11 and 13, respectively, indicating that a single conformer, the sterically unstable endo-aryl-endo-cyanostyryl carbonyl ylide 14 (15), is initially formed in the reaction of 1 with 2. It was concluded that the endo-vinyl-exo-aryl vinylcarbonyl ylides 17a-c arising from 2a-c undergo disrotatory cylization to exclusively produce 5, whereas the ylides 17d,e arising from 2d,e undergo partly symmetry-forbidden conrotaory cyclization to sterically stable trans-diaryldihydrofurans 6d,e as well as the symmetry-allowed process to 5d,e.

Synthesis of Heterocyclic Compounds by Carbenoid Transfer Reactions

“…The polycyclic systems were obtained and the rhodium catalyst recovered and re-used. In a recent report, Hamaguchi and co-workers [107] showed that both oxiranes (198) and dihydrofurans (199) could be formed nonstereospecifically from vinylcarbonyl ylides (Scheme 32) [108]. On the other hand, Doyle and Timmons reported that phenyldiazoacetate-derived carbonyl and imminium ylides underwent to stereospecific ring closure to form epoxides (201) and aziridines (202), respectively, in high yield (Scheme 31) [109].…”

Chemoselective Carbenoid Reactions of Furan/Thiophene/Pyrrole Ring Containing Carbonyl and Conjugated Carbonyl at Their 2‐Positions

“…Moreover, a formal [6+1] addition reaction to yield dihydrobenzoxepines along with dihydrofurans was reported previously . Afterwards, copper‐catalyzed formal‐[4+1]/[5+1] cyclizations were widely investigated …”

Highly Stereoselective Syntheses of Five- and Seven-Membered Ring Heterocycles from Ylides Generated by Catalytic Reactions of Styryldiazoacetates with Aldehydes and Imines

“…Given the facility with which these reactions occur and their apparent stereospecificity, we have continued our investigations. Prompted by a recent report that both dihydrofurans and oxiranes are formed nonstereospecifically from vinylcarbonyl ylides (Scheme ), we now report the extension of ylide transformations with styryldiazoacetates to five- and seven-membered ring heterocycles with high or complete stereocontrol

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