2023
DOI: 10.1021/acs.orglett.3c01166
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DBU-Catalyzed Ring Expansion or Ene-amine Formation Involving δ-Acetoxy Allenoates and N-Sulfonyl Hydrazides

Abstract: DBU-catalyzed spiro-annulation and concomitant ring expansion/domino reaction of δ-acetoxy allenoates with cycl-2-ene-N-sulfonyl hydrazides afford ring-expanded (5 → 6, 6 → 7, and 7 → 8) products. By contrast, cycl-3-ene/ane-N-sulfonyl hydrazones under similar conditions deliver pyrazole cores with the same allenoate that involves allylic elimination in which δ-acetoxy allenoate serves as 3C-synthon. The key spirocyclic intermediates, as well as dienyl-amine intermediates, are isolated and characterized. An ex… Show more

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Cited by 10 publications
(7 citation statements)
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“…We then examined DMAP analogues 4-PPY and 4-APY (entries 13–14); while 4-PPY and DABCO gave a lower yield, 4-APY was ineffective. Use of DBU afforded the previously reported pyridine derivative (entry 16) . Lowering the amount of DMAP from 20 to 10 mol % decreased the yield (entry 17).…”
Section: Results and Discussionmentioning
confidence: 84%
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“…We then examined DMAP analogues 4-PPY and 4-APY (entries 13–14); while 4-PPY and DABCO gave a lower yield, 4-APY was ineffective. Use of DBU afforded the previously reported pyridine derivative (entry 16) . Lowering the amount of DMAP from 20 to 10 mol % decreased the yield (entry 17).…”
Section: Results and Discussionmentioning
confidence: 84%
“…In the past few decades, allenes have been extensively explored in cyclization reactions. , Among the substituted allenes, allenoates have found numerous applications in Lewis base-directed cycloaddition/annulation reactions via zwitterionic intermediates by taking Lu’s [3 + 2] cycloaddition as an inspirational finding. The readily detachable -OAc group in acetoxy allenoates renders this class of compounds as valuable synthons by generating key diene-ammonium/phosphonium intermediates . In Lewis base-mediated/catalyzed annulations, δ-acetoxy allenoates can offer 5–8-membered ring scaffolds by the attack of the nucleophile at the δ- or α-carbon of an electrophilic intermediate, wherein the allenoate part offers 1C - 4C for the framework, but so far none of them utilized acetoxy allenoates as 5C- synthons (Scheme a–b) .…”
Section: Introductionmentioning
confidence: 99%
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“…As anticipated, the desired product 7a was formed in 94% yield. It is noteworthy to mention that DBU has been employed as a nucleophilic base in numerous reactions of allenoates . Also, it was utilized for the isomerization of alkynoates into trisubstituted allenoates .…”
mentioning
confidence: 99%
“…Afterwards, γ-addition/[3+2] and [3+2]/[3+2] domino annulation reactions involving β′-acetoxy allenoates and electron donor–acceptor amphiphilic compounds were published sequentially by Tong 18 and Shi, 19 in which allenes performed as C4 synthons as well (Scheme 1b). Additionally, the acetoxy tethered allenoates could function as C3 synthons activated by tertiary phosphines or amines to interact with dinucleophiles with [3+2] 20 or [3+3] 21 cyclizations occurring (Scheme 1c). Interestingly, a sequential phosphine-catalyzed domino [4+2] annulation was disclosed by the Huang group, in which β′-acetoxy allenoates were employed as C2 synthons (Scheme 1d).…”
mentioning
confidence: 99%