Interconversions of heterocycles containing S, N, and O

Fentanyl-Related Compounds and Derivatives: Current Status and Future Prospects for Pharmaceutical Applications

“…Obtained data indicate that only 3-methylation has a major effect for enhancing analgesic potency, whereas 2-methyl or 2,5-dimethyl substitution is detrimental to analgesic activity. However, comparison with data obtained by other groups suggested this data may not be correct [84–88]. …”

“…Except for the known (±)- cis -3-methylfentanyl and the novel (±)- cis -3-ethylfentanyl, the others were inactive or less active than fentanyl itself. The synthesis of 2.5-dimethyl-fentanyl – phenaridine ( 29 ) – started with 2-methylhex-5-en-3-yn-2-ol was described (Supplementary Information 6) [84,85]. …”

endo/exo Stereoselectivity in DielsAlder Reactions of α,β‐Dialkylated Conjugated Enals to Cyclic 1,3‐Dienes: Intermediates in the Synthesis of (−)‐β‐Santalol and Its Analogs

“…When a mixture of methylcyclopenta-1,3-diene 9 was treated under the same conditions, a major regioisomer exo-10a was isolated (46% yield; exo/endo 57 : 27; Table 1, Entry 56), together with a minor stereoisomer, which, after purification and analysis, turned out to be the corresponding cis-endo-10a stereoisomer 6 ). Once again we were surprised, since we had not observed any (E/Z) isomerization of the dienophile during the cycloaddition, thus suggesting that isomer (Z)-5a is more reactive than its (E)-congener.…”

“…For a single example of the use of a,b-dialkylated monocarbonyl dienophile, see [14c]. 6 ) When catalyzed with 0.1 mol-equiv. of either BF 3 · OEt 2 or AlCl 3 in CH 2 Cl 2 at À 208 to 208, cycloadditions of 3 to either 7 or 9 failed to give the desired cycloadducts.…”