The Synthesis of Naphthalenes and Biaryls
This chapter initially outlines the literature methods for the synthesis of naphthalene and biaryl ring systems, then describes our synthetic efforts towards the synthesis of biaryl and naphthalene derivatives. The reactions of a range of β-keto ester sub
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The Synthesis of Naphthalenes and Biaryls
3.1 Introduction This chapter initially outlines the literature methods for the synthesis of naphthalene and biaryl ring systems, then describes our synthetic efforts towards the synthesis of biaryl and naphthalene derivatives. The reactions of a range of b-keto ester substituted stilbenes with phenylselenenyl chloride and several Lewis acids are described, obtaining biaryls in good to excellent yields.
3.2 Aims of the Project The compounds illustrated in Figs. 3.1 and 3.2 are of interest from a structural viewpoint, but they also have a range of potentially useful biological properties. Biaryl derivatives have stimulated considerable interest within the synthetic chemistry community as a result of their widespread occurrence in nature and their associated biological activities. Despite the presence of some literature procedures, there continues to be a demand for novel methods for biaryl synthesis while there is little literature precedence for the synthesis of 4-arylnaphthol derivatives. With an aim to develop a practical carbon–carbon bond forming process, we describe the concept of a novel C–C bond formation and its application in the synthesis of carbocycles. Our development of a chemical synthesis of these compounds using a wide range of stilbene substrates has been described in Chap. 2. This enables us to extend the scope to other carbocycles. The aim of this project was the selenium- mediated synthesis of challenging biaryls (Scheme 3.1). We proposed linear 1,3-dicarbonyl stilbenes as precursors which would allow the synthesis of biologically important analogues of naphthalenes and biaryls using a combination of a selenium electrophile and a Lewis acid. Upon changing the substitution pattern on the stilbene, we could enhance the reactivity and selectivity in these reactions to S. A. Shahzad, Novel Selenium-Mediated Rearrangements and Cyclisations, Springer Theses, DOI: 10.1007/978-3-642-33173-2_3, Springer-Verlag Berlin Heidelberg 2013
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3 The Synthesis of Naphthalenes and Biaryls OMe OR
OR
OR
OH
COCH3 RO
CH3
COCH3 MeO
R2
CH3
OR 1 OR 177 OH
R = H, 175 R = COMe, 176
R = H, 173 R = COMe, 174
OMe
OMe
CHO CO2CH 3
OMe
O 2N
178
NO2 OMe
NO2 OMe
OH
OMe NO 2
O 2N OH
OH 179
OMe NO 2 180
182
181
183
Fig. 3.1 Naphthalene-containing natural products
OH
OH HO HO
Me
O O
OH COCH 3
OH
HO HO
OH OH OH OH
O
O
OH COCH3
HOOC
CH3 186
185
OH
OH
HO
O O
O
R = Cl,189
CHO OH
R HO CHO OH
R = COMe, 188 187
OH
OH
OH
OH O OH
O OH
O O OH
184
HO HO
HO HO
HO HO
OH
O O OH
CH 3 OH O
OH
OH
CH3 Cl
190
Fig. 3.2 Naphthalene and biaryl glycosides
deliver the desired cyclic products. Thus, selenium electrophile-mediated cyclisation reactions of b-keto ester substituted alkenes of type 240 could generate the desired products 242 and 243. This scenario assumes a one-pot process involving the activation of the alkene and the attack of the internal nucleophile. Because of its cationic character, the seleniranium intermediate could
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