“…In turn, 7 is formed by acylation of aniline 8 by acid 9 . Our recent work on radical cyclizations and ortho -alkenyl anilides 6 and the early studies by several groups of radical annulations of monovinylcyclopropanes 7,8 supported the feasibility of this retrosynthetic analysis.…”
The first stereoselective synthesis of epimeloscine is accomplished in a longest linear sequence of 10 steps and with 13 total steps. The core of the synthesis takes only five steps, the key ones being acylation, stereoselective tandem radical cyclization of a divinylcyclopropane to make two rings, and group selective RCM of the resulting divinylcyclopentane to make the last ring.
“…In turn, 7 is formed by acylation of aniline 8 by acid 9 . Our recent work on radical cyclizations and ortho -alkenyl anilides 6 and the early studies by several groups of radical annulations of monovinylcyclopropanes 7,8 supported the feasibility of this retrosynthetic analysis.…”
The first stereoselective synthesis of epimeloscine is accomplished in a longest linear sequence of 10 steps and with 13 total steps. The core of the synthesis takes only five steps, the key ones being acylation, stereoselective tandem radical cyclization of a divinylcyclopropane to make two rings, and group selective RCM of the resulting divinylcyclopentane to make the last ring.
“…On the other hand, recent rapid growth in the synthetic application of α,β-unsaturated acyl radicals produced by vinyl radical carbonylation 4-6 has posed intriguing mechanistic questions surrounding the roles that α-ketenyl radical isomers play in the chemistry of the corresponding α,β-unsaturated acyl radicals. For example, Pattenden and co-workers have shown (Scheme ) 7 that radicals formed by reaction of phenylseleno esters react exclusively via the α-ketenyl form and these radicals can be trapped efficiently by rapid intramolecular radical reactions such as 5-exo cyclization (eq 1) 7a and cyclopropylcarbinyl radical ring opening (eq 2) 7b 1 2 Isomerization Behaviors of α,β-Unsaturated Acyl Radicals in Tandem Radical Reactions via Noncarbonylation Route …”
[reaction: see text] Ab initio calculations using 6-311G**, cc-pVDZ, aug-cc-pVDZ, and a (valence) double-zeta pseudopotential (DZP) basis set, with (QCISD, CCSD(T)) and without (UHF) the inclusion of electron correlation, and density functional methods (BHandHLYP, B3LYP) predict that alpha,beta-unsaturated acyl radicals and alpha-ketenyl radicals exist as isomers. At the CCSD(T)/cc-pVDZ//BHandHLY/cc-pVDZ level of theory, energy barriers of 15.1 and 17.7-21.7 kJ mol(-)(1) are calculated for the isomerization of s-trans-propenoyl and s-trans-crotonoyl radical to ketenylmethyl and 1-ketenylethyl radical, respectively. Similar results are obtained for the reactions of s-trans isomers involving silyl, germyl, and stannyl groups with energy barriers (DeltaE++) of 12.2-12.4, 13.1-13.9, and 12.9-18.2 kJ mol(-)(1) at the CCSD(T)/DZP//BHandHLYP/DZP calculation, respectively. These results suggest that alpha,beta-unsaturated acyl radicals and alpha-ketenyl radicals are not canonical forms but are isomeric species that can rapidly interconvert.
Introduction
The Preparation of Novel Trialkylgermanes and Stannanes
Trialkyltin Hydrides as Reagents in Radical Chain Reactions
Trialkyltin Hydrides in Non‐Radical Chemistry
Trialkylgermanium and Lead Hydrides in Synthesis
Acknowledgement
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