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Showing posts with label [4]Dendralenes. Show all posts
Showing posts with label [4]Dendralenes. Show all posts

Saturday 30 January 2016

Synthesis and Diels–Alder Reactivity of Substituted [4]Dendralenes





Figure
Scheme 1. Diene-Transmissive Diels–Alder Cycloaddition Sequences of [3]- and [4]Dendralene with the Prototypical Olefinic Dienophile


Abstract Image



The first synthesis of all five possible monomethylated [4]dendralenes has been achieved via two distinct synthetic strategies. The Diels–Alder chemistry of these new dendralenes (as multidienes) with an electron poor dienophile, N-methylmaleimide (NMM), has been studied. Thus, simply upon mixing the dendralene and an excess of dienophile at ambient temperature in a common solvent, sequences of cycloadditions result in the rapid generation of complex multicyclic products. Distinct product distributions are obtained with differently substituted dendralenes, demonstrating that dendralene substitution influences the pathway followed, when a matrix of mechanistic possibilities exists. Dendralene site selectivities are traced to electronic, steric and conformational effects, thereby allowing predictive tools for applications of substituted dendralenes in future synthetic endeavors.

Figure

Scheme 2. Diene-Transmissive Diels–Alder Cycloaddition Sequences of [4]Dendralene (1) with the Dienophile N-Methylmaleimide (NMM)




Figure

Scheme 3. Syntheses of the Five Mono-Methyl-Substituted-[4]Dendralenes


3 Diels-Alder reactions in 1 go

 DIELS ALDER CASCADE 01.29.2016.gif
FROM https://naturalproductman.wordpress.com/2016/01/29/11137/









Tris-adduct 36
An analytic sample of 36 was obtained by recrystallization from EtOAc/hexane to give colorless needles, mp 255–257 °C; Rf 0.20 (EtOAc, 100%);  
1H NMR (300 MHz, CDCl3) δ 3.22 (dd, J = 8.6, 5.9 Hz, 1H), 3.19–3.07 (m, 3H), 3.04–2.91 (m, 5H), 2.90 (s, 6H), 2.86 (s, 3H), 2.65 (ddd, J = 14.1, 13.4, 5.4 Hz, 1H), 2.35 (ddd, J = 14.3, 5.0, 2.5 Hz, 1H), 2.16–2.05 (m, 2H), 2.03–1.91 (m, 1H), 1.85–1.74 (m, 1H), 1.54 (d, J = 6.8 Hz, 3H) ppm;  
13C NMR (75 MHz, CDCl3) δ 179.7 (C), 178.5 (C), 178.4 (C), 178.3 (C), 177.0 (C), 176.6 (C), 130.8 (C), 130.8 (C), 44.4 (CH), 43.4 (CH), 40.8 (CH), 40.6 (CH), 40.3 (CH), 39.2 (CH), 38.8 (CH), 33.7 (CH), 29.0 (CH), 25.0 (CH3), 24.9 (CH3), 24.8 (CH3), 24.7 (CH2), 24.4 (CH2), 23.1 (CH2), 16.5 (CH3) ppm; 
IR (KBr disc) νmax = 2961, 2948, 2842, 1770, 1695, 1435, 1383, 1286 cm–1
LRMS (70 eV, EI) m/z (%) 453 ([M]+•, 100%), 438 (7), 342 (33), 256 (14), 112 (39); 
HRMS calc for C24H27N3O6 [M]+• 453.1900, found 453.1905.

Synthesis and Diels–Alder Reactivity of Substituted [4]Dendralenes

Research School of Chemistry, The Australian National University, Canberra, ACT 2601, Australia
School of Chemistry, The University of New South Wales, Sydney, NSW 2052, Australia
J. Org. Chem., Article ASAP
DOI: 10.1021/acs.joc.5b02583
Publication Date (Web): January 12, 2016
Copyright © 2016 American Chemical Society
ACS Editors' Choice - This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes.
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