Synthesis of C1-substituted 7-oxanorbornadienes

Article abstract of DOI:10.1080/00397911.2011.596640

7-Oxanorbornadienes are valuable synthetic intermediates as they can serve as general templates to create highly substituted ring systems. However, to date, only very few C1-substituted 7-oxanorbornadienes have been synthesized and can be found in the literature. In this article, synthesis of some C1-substituted 7-oxanorbornadienes was achieved by the Diels-Alder reaction between 2-substituted furans and dimethylacetylene dicarboxylate. Moderate to good yields (13-85%) of the Diels-Alder reactions were observed. These C1-substituted 7-oxanorbornadienes will find applications as valuable synthetic intermediates and are useful in the studies of transition-metal-catalyzed reactions.

Full text of DOI:10.1080/00397911.2011.596640

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Synthesis of C1-Substituted 7-
Oxanorbornadienes
Mohammed-Abdul Raheem a & William Tam a
a Guelph-Waterloo Centre for Graduate Work in Chemistry and
Biochemistry, Department of Chemistry , University of Guelph ,
Guelph , Ontario , Canada
Accepted author version posted online: 01 Feb 2012.Published
online: 18 Oct 2012.
To cite this article: Mohammed-Abdul Raheem & William Tam (2013) Synthesis of C1-Substituted 7-
Oxanorbornadienes, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 43:2, 260-267, DOI: 10.1080/00397911.2011.596640
To link to this article: http://dx.doi.org/10.1080/00397911.2011.596640
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Synthetic Communications1, 43: 260–267, 2013
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2011.596640
SYNTHESIS OF C1-SUBSTITUTED
7-OXANORBORNADIENES
Mohammed-Abdul Raheem and William Tam
Guelph-Waterloo Centre for Graduate Work in Chemistry and Biochemistry,
Department of Chemistry, University of Guelph, Guelph, Ontario, Canada
GRAPHICAL ABSTRACT
Abstract 7-Oxanorbornadienes are valuable synthetic intermediates as they can serve as
general templates to create highly substituted ring systems. However, to date, only very
few C1-substituted 7-oxanorbornadienes have been synthesized and can be found in the litera-
ture. In this article, synthesis of some C1-substituted 7-oxanorbornadienes was achieved by
the Diels–Alder reaction between 2-substituted furans and dimethylacetylene dicarboxylate.
Moderate to good yields (13–85%) of the Diels–Alder reactions were observed. These
C1-substituted 7-oxanorbornadienes will find applications as valuable synthetic intermediates
and are useful in the studies of transition-metal-catalyzed reactions.
Keywords Bicyclic alkenes; Diels–Alder reaction; dimethylacetylene dicarboxylate;
furan; 7-oxanorbornadienes
INTRODUCTION
7-Oxanorbornadiene 1 is a valuable synthetic intermediate as it can serve as a
general template to create highly substituted ring systems.[1,2] For instance, asymmet-
ric ring opening of these alkenes allows for the formation of several stereocenters in a
single step.[2–5] We have recently investigated different modes of transition-metal-
catalyzed reactions of oxanorbornadiene 1 and found that depending on the reaction
conditions, several products (2–7) could be obtained (Scheme 1). For example, when
7-oxanorbornadiene 1 is treated with an alkyne in the presence of the ruthenium cata-
lyst, CpꢀRu(COD)Cl, a [2 þ 2] cycloaddition is observed and cyclobutene cycloadduct
2 is formed.[6,7] When oxanorbornadiene 1 is treated with the secondary propargylic
alcohol 8 in the presence of the neutral Ru catalyst, CpꢀRu(COD)Cl, in MeOH or
Received June 6, 2011.
Address correspondence to William Tam, Guelph-Waterloo Centre for Graduate Work in
Chemistry and Biochemistry, Department of Chemistry, University of Guelph, Guelph, Ontario, N1G
2W1, Canada. E-mail: wtam@uoguelph.ca
260

SYNTHESIS OF C1-SUBSTITUTED 7-OXANORBORNADIENES
261
Scheme 1. Transition-metal–catalyzed reactions of oxabenzonorbornadiene 1.
using a cationic Ru catalyst (e.g., [CpRu(CH3CN)3]PF6), isochromene 3 is formed.[8,9]
On the other hand, if the same reaction between oxanorbornadiene 1 and the second-
ary propargylic alcohol 8 is carried out with CpꢀRu(COD)Cl in tetrahydrofuran
(THF), cyclopropane 4 is produced.[10] More recently, we have observed that in the
absence of an alkyne, CpꢀRu(COD)Cl catalyzes the isomerization of oxanorborna-
diene 1 to the corresponding naphthalene oxide 5 or naphthol 6.[11,12] We have also
Scheme 2. Synthesis of 2-phenylfuran 9d and 2-trimethylfuran 9 h.

262
M.-A. RAHEEM AND W. TAM
Table 1. Synthesis of C1-substituted 7-oxanorbornadienes
Entry
1
Furan
Product
Yield (%)a
85
2
3
4
85
34
42
5
6
7
8
37
50
13
75
51
9
10
35
(Continued )

SYNTHESIS OF C1-SUBSTITUTED 7-OXANORBORNADIENES
263
Table 1. Continued
Entry
11
Furan
Product
Yield (%)a
0 (92)b
aIsolated yield after column chromatography.
bCompound 11k was unstable and was aromatized to form compound 12 in 92% (see Scheme 3).
reported that asymmetric cationic rhodium(I)-catalyzed cyclodimerization of oxanor-
bornadiene 1 produces dimers 7 in excellent enantioselectivity (up to 99% ee).[13]
Because 7-oxanorbornadiene 1 is symmetrical, no regiochemical information
could be gained from these studies. To explore the regioselectivity of these reactions,
unsymmetrical 7-oxanorbornadienes needed to be synthesized. To our surprise, a
search in the literature has shown that very few C1-substituted 7-oxanorbornadienes
have been synthesized to date.[14] In this article, we report the synthesis of some
C1-substituted 7-oxanorbornadienes 11 by the Diels–Alder reaction between
2-substituted furans 9 and dimethylacetylene dicarboxylate 10.
RESULTS AND DISCUSSION
2-Substituted furans 9a–c, 9e–g, and 9i are commercially available. 2-Phenyl-
furan 9d was prepared in 73% yield by recently reported Pd-catalyzed Suzuki coupling
reaction between 2-bromofuran and phenyl boronic acid,[15] and furan-2-yltrimethyl-
silane 9j was synthesized in 62% yield by deprotonation of furan followed by trapping
with chlorotrimethylsilane[16] (Scheme 2). With the 2-substituted furans 9a–i in hand,
we studied the Diels–Alder reactions of these 2-substituted furans with dimethylace-
tylene dicarboxylate 10, and the results are shown in Table 1.
C1-Substituted 7-oxanorbornadienes 11a and 11b with primary alkyl group
(Y Me and Et) were produced in excellent yields (85%, Table 1, entries 1 and 2).
=
The yields of the Diels–Alder reactions were significantly lowed with a tertiary alkyl
t
=
group (11c, Y ¼ Bu, 34%) or with an aromatic group (11d, Y Ph, 42% (entries 3–4).
=
With carbonyl substituents (ester 11e, Y COOMe; ketone 11f, Y COMe; and
=
=
amide 11 g, Y CONH2), poor to moderate yields of the Diels–Alder reactions were
observed (13–50% yields, entries 5–7). C1-Substituted 7-oxanorbornadienes 11 h and
=
11i with a primary alcohol and protected primary amine group (Y CH2OH and
CH2NHAc) were produced in good yields (75% and 51%, entries 8 and 9). Note that
the Diels–Alder reaction with a nonprotected free primary amine group (CH2NH2)
led to a complicated mixture of products and decomposition was observed. C1-Silyl
substituted 7-oxanorbornadienes 11j can also be produced in 35% yield (entry 10).
However, C1-methoxy substituted 7-oxanorbornadiene 11k was found to be
unstable and was aromatized to phenol 12k in 92% yield (Table 1, entry 11, and
Scheme 3). We have attempted the Diels–Alder reactions of 2-substituted furans with
=
Y CN, NO2, COOH, and Br, but in all these cases, complicated mixtures, of
products were obtained, decomposition was observed, and no desired C1-substituted
7-oxanorbornadienes were isolated.

264
M.-A. RAHEEM AND W. TAM
Scheme 3. Reaction of 9k and 10.
CONCLUSION
In conclusion, we have synthesized of some C1-substituted 7-oxanorborna-
dienes 11a–11j, by the Diels–Alder reaction between 2-substituted furans 9a–9j and
dimethylacetylene dicarboxylate 10. Moderate to good yields (13–85%) of the
Diels–Alder reactions were observed. These C1-substituted 7-oxanorbornadienes will
find applications as valuable synthetic intermediates and are useful in the studies of
transition-metal-catalyzed reactions. Regioselectivity studies of different transition-
metal-catalyzed reactions (such as those indicated in Scheme 1) of these C1-substituted
7-oxanorbornadienes 11a–11j will be reported in the near future.
EXPERIMENTAL
All reactions are done in septum-sealed, flame-dried flasks under a nitrogen
atmosphere. All commercial reagents were used as received from their respective
suppliers. Reagent-grade furan and N-bromosuccinimide (NBS) purchased from
1
Aldrich were used without additional purification. H NMR and 13C NMR spectra
were recorded at 300=400 and 75=100 MHz, respectively. Chemical shifts are reported
in parts per million (d) using internal solvent signals as references, and coupling
constants are reported in hertz (Hz).
General Procedure for the Diels–Alder Reaction Between
2-Substituted Furans 9a–9j and Dimethylacetylene Dicarboxylate 10
The 2-substituted furan (1.1 eq.) was slowly charged into dimethylacetylene
dicarboxylate (1.0 eq.) at room temperature. The resulting solution was heated to
90–100 ꢁC in a screw-capped vial for 12–16 h. Reaction completion was monitored
by thin-layer chromatography (TLC). The crude product was directly purified by
column chromatography (EtOAc–hexanes mixtures) to give the product.
1-Methyl-2,3-dimethoxycarbonyl-7-oxanorbornadiene, 11a
Rf ¼ 0.40 (EtOAc–hexanes, 1:4); IR (CH2Cl2): 2955, 1716, 1641, 1473, 1267,
1
1132 cmꢂ1; H NMR (CDCl3, 400 MHz): d 1.76 (s, 3H), 3.76 (s, 3H), 3.82 (s, 3H),
5.58 (d, J ¼ 2.0 Hz, 1H), 6.96 (d, J ¼ 5.2 Hz, 1H), 7.16 (dd, J ¼ 5.2, 1.6 Hz, 1H); 13C
(APT) NMR (CDCl3, 100 MHz): 15.1 (CH3), 52.2 (CH3), 52.3 (CH3), 83.3 (CH),
93.9 (qC), 144.6 (CH), 145.9 (CH), 151.2 (qC), 156.5 (qC), 162.8 (qC), 164.9 (qC).
HRMS (CI) calcd. for C11H13O5 (M þ H): 225.0763; found: 225.0770.

SYNTHESIS OF C1-SUBSTITUTED 7-OXANORBORNADIENES
265
1-Ethyl-2,3-dimethoxycarbonyl-7-oxanorbornadiene, 11b
Rf ¼ 0.40 (EtOAc–hexanes, 1:4); IR (CH2Cl2): 2955, 1726, 1639,1437, 1273,
1
1122 cmꢂ1; H NMR (CDCl3, 400 MHz): d 0.99 (t, J ¼ 7.4 Hz, 3H), 2.07–2.22 (m,
2H), 3.74 (s, 3H), 3.81 (s, 3H), 5.62 (d, J ¼ 1.9 Hz, 1H), 6.95 (d, J ¼ 5.2 Hz, 1H),
7.15 (dd, J ¼ 5.2, 1.9 Hz, 1H); 13C (APT) NMR (CDCl3, 100 MHz): 9.0 (CH3),
21.9 (CH2), 52.2 (CH3), 52.3 (CH3), 83.2 (CH), 98.4 (qC), 144.7 (CH), 144.8 (CH),
151.4 (qC), 156.2 (qC), 162.7 (qC). 165.3 (qC). HRMS (CI) calcd. for C12H15O5
( M þH): 239.0919; found: 239.0926.
1-tert-Butyl-2,3-dimethoxycarbonyl-7-oxanorbornadiene, 11c
Rf ¼ 0.26 (EtOAc–hexanes, 1:5); IR (CH2Cl2): 2957, 1717, 1634, 1482, 1399,
1
1273, 1201 cmꢂ1; H NMR (CDCl3, 300 MHz): d 1.08 (s, 9H), 3.71 (s, 3H), 3.82
(s, 3H), 5.62 (d, J ¼ 1.6 Hz, 1H), 7.10 (d, J ¼ 5.3 Hz, 1H), 7.16 (dd, J ¼ 5.3, 1.6 Hz,
1H); 13C (APT) NMR (CDCl3, 75 MHz): 26.3 (3 ꢃ CH3), 32.8 (qC), 52.1 (CH3),
52.5 (CH3), 82.3 (CH), 105.7 (qC), 142.8(CH), 145.2 (CH), 149.6 (qC), 159.3 (qC),
162.3 (qC), 167.8 (qC). HRMS (CI) calcd. for C14H19O5 (M þ H): 267.1232; found:
267.1233.
1-Phenyl-2,3-dimethoxycarbonyl-7-oxanorbornadiene, 11d
Rf ¼ 0.31 (EtOAc–hexanes, 1:4); IR (CH2Cl2): 2955, 1717, 1700, 1635, 1436,
1
1362, 1286, 1238 cmꢂ1; H NMR (CDCl3, 300 MHz): d 3.62 (s, 3H), 3.77 (s, 3H),
5.82 (d, J ¼ 1.9 Hz, 1H), 7.31 (dd, J ¼ 5.2, 1.9 Hz, 1H), 7.44–7.33 (m, 4H), 7.50 (m,
2H); 13C (APT) NMR (CDCl3, 75 MHz): 51.9 (CH3), 52.1 (CH3), 83.4 (CH), 97.8
(qC), 126.6 (CH), 128.4 (CH), 128.7 (CH), 133.6 (qC), 143.9 (CH), 144.8 (CH),
149.0 (qC), 158.5 (qC), 162.2 (qC), 164.8 (qC).
1,2,3-Trimethoxycarbonyl-7-oxanorbornadiene, 11e
Rf ¼ 0.48 (EtOAc–hexanes, 1:1); IR (CH2Cl2): 3008, 2957, 2851, 1741, 1644,
1
1438, 1269, 1204, 1148 cmꢂ1; H NMR (CDCl3, 400 MHz): d 3.78 (s, 3H), 3.79 (s,
3H), 3.87 (s, 3H), 5.72 (d, J ¼ 2.1 Hz, 1H), 7.25–7.29 (m, 2H); 13C (APT) NMR
(CDCl3, 100 MHz): 52.5 (CH3), 52.6 (CH3), 53.1 (CH3), 84.6 (CH), 94.0 (qC),
142.2 (CH), 144.3 (CH), 150.8 (qC), 153.6 (qC), 162.3 (qC), 162.9 (qC), 166.0
(qC). HRMS (CI) calcd. for C12H13O7 (M þ H): 269.0661; found: 269.0666.
1-Methylcarbonyl-2,3-dimethoxycarbonyl-7-oxanorbornadiene, 11f
Rf ¼ 0.26 (EtOAc–hexanes, 1:5); IR (CH2Cl2): 2957, 1738, 1723, 1717, 1645,
1
1436, 1268, 1116 cmꢂ1; H NMR (CDCl3, 400 MHz): d 2.30 (s, 3H), 3.76 (s, 3H),
3.78 (s, 3H), 5.72(d, J ¼ 1.8 Hz, 1H), 7.20 (d, J ¼ 5.2 Hz, 1H), 7.24 (dd, J ¼ 5.2,
1.8 Hz, 1H); 13C (APT) NMR (CDCl3, 100 MHz): 26.6 (CH3), 52.4 (CH3), 52.6
(CH3), 84.0 (CH), 99.2 (qC), 141.9 (CH), 144.3 (CH), 149.7 (qC), 154.6 (qC),
162.3 (qC),163.3 (qC), 201.7 (qC). HRMS (CI) calcd. for C12H13O6 (M þ H):
253.0712; found: 253.0719.

266
M.-A. RAHEEM AND W. TAM
1-Aminocarbonyl-2,3-dimethoxycarbonyl-7-oxanorbornadiene, 11g
Rf ¼ 0.46 (EtOAc–hexanes, 1:1); IR (CH2Cl2): 3177, 2955, 1717, 1669, 1433,
1
1297, 1254, 1202 cmꢂ1; H NMR (CDCl3, 300 MHz): d 3.75 (s, 3H), 3.83 (s, 3H),
5.73 (d, J ¼ 1.9 Hz, 1H), 5.98 (brs, 1H), 6.28 (brs, 1H), 7.23 (dd, J ¼ 5.2, 1.9 Hz,
1H), 7.29 (d, J ¼ 5.2 Hz, 1H), 13C (APT) NMR (CDCl3, 75 MHz): 52.4 (CH3),
52.7 (CH3), 83.5 (CH), 94.8 (qC), 142.8 (CH), 143.9 (CH), 147.5 (qC), 155.8 (qC),
162.1 (qC), 163.8 (qC), 167.4 (qC). HRMS (CI) calcd. for C11H12NO6 (M þ H):
254.0665; found: 254.0660.
1-Hydroxymethyl-2,3-dimethoxycarbonyl-7-oxanorbornadiene, 11h
Rf ¼ 0.16 (EtOAc–hexanes, 1:1); IR (CH2Cl2): 3493, 2955, 1716, 1637, 1438,
1
1302, 1271 cmꢂ1; H NMR (CDCl3, 400 MHz): d 3.78 (s, 3H), 3.82 (s, 3H), 4.25
(ABq, 2H), 5.65 (d, J ¼ 1.8 Hz, 1H), 7.03 (d, J ¼ 5.3 Hz, 1H), 7.22 (dd, J ¼ 5.3,
1.8 Hz, 1H); 13C (APT) NMR (CDCl3, 100 MHz): 52.3 (CH3), 52.5 (CH3), 59.9
(CH2), 83.9 (CH), 98.3 (qC), 142.5 (CH), 144.9 (CH), 152.6 (qC), 153.6 (qC),
162.9 (qC), 164.6 (qC). HRMS (CI) calcd. for C11H13O6 (M þ H): 241.0712; found:
241.0719.
1-Acetylaminomethyl-2,3-dimethoxycarbonyl-7-oxanorbornadiene, 11i
Rf ¼ 0.24 (EtOAc pure); IR (CH2Cl2): 3390, 2954, 1716, 1674, 1530, 1436,
1
1267, 1124 cmꢂ1; H NMR (CDCl3, 300 MHz): d 1.92 (s, 3H), 3.74 (s, 3H), 3.77
(s, 3H), 3.85–4.14 (m, 2H), 5.59 (d, J ¼ 1.7 Hz, 1H), 5.96 (brs, 1H), 6.95 (d,
J ¼ 5.3 Hz, 1H), 7.17 (dd, J ¼ 5.2, 1.6 Hz, 1H); 13C (APT) NMR (CDCl3,
75 MHz): 23.0 (CH3), 37.8 (CH2), 52.4 (CH3), 52.6 (CH3), 83.7 (CH), 96.9 (qC),
142.9 (CH), 145.3 (CH), 152.8 (qC), 153.6 (qC), 162.6 (qC), 163.9 (qC), 170.1 (qC).
1-Trimethylsilyl-2,3-dimethoxycarbonyl-7-oxanorbornadiene, 11j
Rf ¼ 0.4 (EtOAc–hexanes, 1:5); IR (CH2Cl2): 2954, 1717, 1436, 1251, 1111 cmꢂ1
;
1H NMR (CDCl3, 300 MHz): d 0.16 (s, 9H), 3.73 (s, 3H), 3.70 (s, 3H), 5.68 (d,
J ¼ 1.5 Hz, 1H), 7.14 (d, J ¼ 5.2 Hz, 1H), 7.19 (dd, J ¼ 5.2, 1.5 Hz, 1H); 13C (APT)
NMR (CDCl3, 75 MHz): ꢂ3.3 (3 ꢃ CH3), 52.0 (2 ꢃ CH3), 85.3 (CH), 91.5 (qC),
143.3 (CH), 146.1 (CH), 150.4 (qC), 159.3 (qC), 163.0 (qC), 165.7 (qC). HRMS
(CI) calcd. for C13H19SiO5 (M þ H): 283.1002; found: 283.1008.
2,3-Dimethoxycarbonyl-4-methoxyphenol, 12k
Rf ¼ 0.48 (EtOAc–hexanes, 1:1); IR (CH2Cl2); 3145, 3025, 1738, 1677, 1475,
1
1456, 1227, 1119 cmꢂ1; H NMR (CDCl3, 300 MHz): d 3.75 (s, 3H), 3.86 (s, 3H),
3.87 (s, 3H), 6.97 (d, J ¼ 9.2 Hz, 1H), 7.11 (d, J ¼ 9.2 Hz, 1H), 10.44 (s, 1H); 13C
(APT) NMR (CDCl3, 75 MHz): 52.5 (CH3), 52.9 (CH3), 57.2 (CH3) 109.4 (qC),
119.4 (CH), 120.5 (CH), 124.1(qC), 148.8 (qC), 155.6 (qC), 167.4 (qC), 168.9 (qC);
HRMS (CI) calcd. for C11H13O6 (M þ H): 241.0712; found: 241.0719.

SYNTHESIS OF C1-SUBSTITUTED 7-OXANORBORNADIENES
267
ACKNOWLEDGMENTS
This work was supported by Merck Frosst Centre for Therapeutic Research,
Natural Sciences and Engineering Research Council of Canada (NSERC), and
Boehringer Ingelheim (Canada) Ltd.
REFERENCES
1. Rayabarapu, D. K.; Cheng, C.-H. Acc. Chem. Res. 2007, 40, 971–983
2. Lautens, M.; Fagnou, K.; Heibert, S. Acc. Chem. Res. 2003, 36, 48–58.
3. Padwa, A.; Wang, Q. J. Org. Chem. 2006, 71, 7391–7402.
4. Cho, Y.; Zunic, V.; Senboku, H.; Olsen, M.; Lautens, M. J. Am. Chem. Soc. 2006, 128,
6837–6846.
5. Chen, C. L.; Martin, S. F. J. Org. Chem. 2006, 71, 4810–4818
6. Burton, R. R.; Tam, W. J. Org. Chem. 2007, 72, 7333–7336
7. Burton, R. R.; Tam, W. Tetrahedron Lett. 2006, 47, 7185–7189
8. Villeneuve, K.; Tam, W. Eur. J. Org. Chem. 2006, 5499–5435.
9. Villeneuve, K.; Tam, W. Organometallics 2007, 26, 6082–6090.
10. Villeneuve, K.; Tam, W. Organometallics 2006, 25, 843–848.
11. Villeneuve, K.; Tam, W. J. Am. Chem. Soc. 2006, 128, 3514–3515.
12. Ballantine, M.; Menard, M. L.; Tam, W. J. Org. Chem. 2009, 74, 7570–7573
13. Allen, A.; Le Marquand, P.; Burton, R.; Villeneuve, K.; Tam, W. J. Org. Chem. 2007, 72,
7849–7857.
14. Only C1-substituted 7-oxanorbornadienes 11a, b, e, h are known compounds. For 11a: see
Ref. 7; 11b: Fry, A. J.; Sherman, L. R.; Beaulieu, A. R.; Sherwin, C. J. Org. Chem. 1990,
55, 389–391; 11e: see Ref. 6; 11 h: Parsons, P. J.; Montagnon, T., Giles, M.; Hitchcock, P.
Synlett 1999, 1407–1408.
15. Haner, J.; Jack, K.; Nagireddy, J.; Raheem, M. A.; Durham, R.; Tam, W. Synthesis 2011,
5, 731–738.
16. Sofikiti, N.; Tofi, M.; Montagnon, T.; Vassilikogiannakis, G.; Stratakis, M. Org. Lett.
2005, 7, 2357–2359.