By Matthias D'hooghe, Hyun-Joon Ha
The sequence subject matters in Heterocyclic Chemistry offers severe experiences on current and destiny developments within the learn of heterocyclic compounds. total the scope is to hide issues facing all parts inside of heterocyclic chemistry, either experimental and theoretical, of curiosity to the final heterocyclic chemistry neighborhood. The sequence contains subject comparable volumes edited through well known editors with contributions of specialists within the box. All chapters from subject matters in Heterocyclic Chemistry are released on-line First with anyone DOI. In references, themes in Heterocyclic Chemistry is abbreviated as best Heterocycl Chem and mentioned as a journal.
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Extra info for Synthesis of 4- to 7-membered Heterocycles by Ring Expansion: Aza-, oxa- and thiaheterocyclic small-ring systems
P. David Scheme 53 Ring expansion to azepine Ph Ph N H DMDA -20°C, 95 % Ph N H CO2Me CO2Me 201 Ph CN 199 Scheme 54 Ring expansion to bicyclic azepine Ph NH N H 80°C, 6 days 70 % CN 202 O CN 203 O O N Tr N Tr 206 207 Ni(COD)2 5 mol% N N Tr 204 Scheme 55 Ring expansion to bicyclic azepine NH CO2Me CO2Me 200 N N 205 10 mol%, 60°C 6 h 100 %, isomeric ratio 4:1 60°C, 12 h HN N 58 % NO2 208 H NO2 209 NO2 210 204 to nickel(0) in the presence of an NHC ligand 205 and isolated a 4:1 mixture of isomeric furanoazepine 206/207 arising from the alkyne insertion into the C–C bond of the aziridine ring (Scheme 54).
Ring expansion of aziridines leading to six-membered rings through other processes than [2,3] sigmatropic rearrangements are scarce in literature, since, to CO2Et O O N2 Cu(acac)2 N Ph Ph 178 N MeCN, reflux 21% O CO2Et N Ph 179 Ph 180 O N2 Cu(acac)2 C6H6, reflux 24% N 181 Scheme 47 2-Alkenylaziridines react with carbenes to generate nitrogen ylides that expand through a [2,3] sigmatropic rearrangement R1 CO2t-Bu N LDA 182 R2 R1 CO2t-Bu N 183 R2 R1 = CH2OBn, Cy, t-Bu R2 = H, Me Scheme 48 Cu-catalyzed ring expansion into piperidines R1 NH CO2t-Bu R2 184 (92-98%) 24 F.
Alternatively, when the ring expansion was effected without added nucleophile, then 4-iodopyrrolidine 310 was produced, and the secondary iodide could react with azide anion or primary amine through a classical SN2 reaction, to produce trans-2,5 pyrrolidines 311 (Scheme 76). 2,3-trans-Amino pyrrolidines 313 can be produced form ring expansion of anti2-(aminomethyl)azetidines 312 upon treatment with a strong Lewis acid such as BF3 etherate . The mechanism depicted in Scheme 77 involves ring opening of the azetidine ring assisted by the adjacent amino group to give a transient aziridine which further evolves to the more stable 3-aminopyrrolidine 313.
Synthesis of 4- to 7-membered Heterocycles by Ring Expansion: Aza-, oxa- and thiaheterocyclic small-ring systems by Matthias D'hooghe, Hyun-Joon Ha