Lithium 2,2,6,6-tetramethylpiperidide (LiTMP)-mediated alpha- and beta-lithiations of epoxides are described. LiTMP displays a markedly higher reactivity than does lithium diisopropylamide, consistent with literature reports. Detailed rate studies of LiTMP/THF and LiTMP/Me(2)NEt mixtures reveal similar rates but significant mechanistic differences. LiTMP-mediated alpha-lithiation of cis-cyclooctene oxide with subsequent oxacarbenoid formation and transannular C-H insertion proceeds via monosolvated dimers in both THF and Me(2)NEt. LiTMP-mediated beta-lithiation of 2,3-dimethyl-2-butene oxide affords the corresponding allylic alcohol via a monosolvated monomer in THF and a monosolvated dimer in Me(2)NEt. We discuss how the solvent-dependent aggregation of LiTMP markedly influences the rate profile. The reaction transition structures are examined with density functional computations.
The addition of enolates derived from indole-3-acetic esters 1−3 to pyridinium salts 4, 23, and 24, followed by acid cyclization of the resulting 1,4-dihydropyridines, leads to tetrahydro-1,5-methanoazocino[3,4-b]indoles 5−7, 25−27, which have been subsequently elaborated into 4E-ethylidene(or 4α-ethyl)-hexahydro-1,5-methanoazocino[3,4-b]indoles. Closure of the six-membered C ring of akuammiline alkaloids by formation of C-6/C-7 bond from appropriately N (b) -substituted derivatives of these tetracyclic ABDE substructures has been extensively investigated. In the N-unsubstituted indole series, both cyclization of thionium ions generated either by Pummerer reaction from sulfoxide 16 or by DMTSF treatment of dithioacetal 36 and photocyclization of chloroacetamide 47 occur upon the indole nitrogen to give pentacycles 18, 38, and 49, respectively. When the indole nitrogen is blocked by a substituent, the thionium ions derived from sulfoxides 17 and 43 and dithioacetals 37 and 44 do not cyclize and lead to different products depending on the reaction conditions, whereas chloroacetamides 48 and 51 undergo a reductive photodehalogenation. Attempted radical cyclization of seleno derivatives 53, 55, and 56 under a variety of conditions gives the corresponding reduced products. Finally, attempted photoisomerization of 1-acylindole 62 leads to the N (b) -methyl tetracycle 63.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.