1E-Methyl[4]dendralene

1E-Methyl[4]dendralene (10)

A freshly prepared solution of (3-methylenepenta-1,4-dien-2-yl)magnesium chloride (63) (25 mL, 0.16 M solution in THF, 4.0 mmol, 1.6 mol equiv) was added slowly into a stirred solution of ZnBr₂ (0.92 g, 4.1 mmol, 1.6 mol equiv) and THF (5.0 mL) at 0 °C. Once the addition was complete, the reaction mixture was allowed to warm to 25 °C and stirred for a further 20 min. To this was added 1E-bromopropene (19) (0.22 mL, 2.6 mmol, 1.0 mol equiv) followed by addition of Pd(PPh₃)₄ (0.15 g, 0.13 mmol, 0.050 mol equiv) and the reaction mixture was stirred at 25 °C for 16 h with the exclusion of light. The resulting solution was poured into water (0.15 L), stirred for 15 min and petroleum ether (30–40 °C) (0.15 L) was added. The organic phase was separated and aqueous phase was then extracted with petroleum ether (30–40 °C) (2 × 0.10 L). The organic phases were combined, washed with brine, dried over MgSO₄, filtered and concentrated under reduced pressure (50 mbar, 0 °C). Purification by flash column chromatography (SiO₂, petroleum ether (30–40 °C)) gave the title compound 10 (0.11 g, 0.92 mmol, 35%) as a colorless oil.  

R_f 0.56 (petroleum ether (30–40 °C)); 

¹H NMR (300 MHz, CDCl₃) δ 6.41 (ddd, J = 17.4, 10.5, 0.8 Hz, 1H), 6.13 (ddd, J = 15.5, 1.9, 0.7 Hz, 1H), 5.65 (dq, J = 15.6, 5.0 Hz, 1H), 5.24–5.14 (m, 2H), 5.12–5.01 (m, 3H), 4.89 (dd, J = 2.2, 0.8 Hz, 1H), 1.74 (ddt, J = 6.7, 1.5, 0.7 Hz, 3H) ppm;

 ¹³C NMR (75 MHz, CDCl₃) δ 147.5 (C), 146.4 (C), 137.7 (CH), 132.1 (CH), 128.5 (CH), 117.4 (CH₂), 116.5 (CH₂), 115.0 (CH₂), 18.2 (CH₃) ppm;

 IR (thin film) ν_max = 3083, 2954, 2923, 2852, 1635, 1456 cm^–1;

 LRMS (70 eV, EI) m/z (%) 120 ([M]^+•, 15%), 105 (100), 91 (44), 79 (34); 

HRMS calc for C₉H₁₂ [M]^+• 120.0939, found 120.0938.

http://pubs.acs.org/doi/full/10.1021/acs.joc.5b02583








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

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.

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

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

3 Diels-Alder reactions in 1 go

 
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; R_f 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) ν_max = 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

Mehmet F. Saglam^†, Ali R. Alborzi^†, Alan D. Payne^†, Anthony C. Willis^†, Michael N. Paddon-Row^‡, and Michael S. Sherburn^*†

^† 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

*E-mail: michael.sherburn@anu.edu.au.

 http://pubs.acs.org/doi/full/10.1021/acs.joc.5b02583

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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5-Bromo-1-methyl-1H-imidazole-4-carbonitrile

Molecular Formula:	C5H4BrN3
Molecular Weight:	186.00936 g/mol

5-Bromo-1-methyl-1H-imidazole-4-carbonitrile, 3

bromocyanoimidazole 3 (250.2 g, 70% yield) as a white plates (mp 140–147 °C):  

¹H NMR (400 MHz, DMSO-d₆) δ 8.05 (s, 1H), 3.66 (s, 3H);


¹³C NMR (100 MHz, DMSO-d₆) δ 141.4, 115.0, 114.3, 113.4, 33.4;


HRMS-ESI (m/z) calcd for C₅H₅N₃Br [M + H]⁺ 185.9664, found 185.9660

//////n1(cnc(c1Br)C#N)C
 CN1C=NC(=C1Br)C#N