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Steps towards a practical synthesis of macrocyclic bisbenzylisoquinolines

Al-Hiari, Yusuf M. and Bennett, Stephen J. and Cox, Brian and Davies, Robert J. and Khalaf, Abedawn I. and Waigh, Roger D. and Worsley, Alan J. (2005) Steps towards a practical synthesis of macrocyclic bisbenzylisoquinolines. Journal of Heterocyclic Chemistry, 42 (4). pp. 647-659. ISSN 0022-152X

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Abstract

Tetrahydrooxathiadiazapentacene I is prepd. as a potential intermediate for the prepn. of bisbenzylisoquinoline macrocycles, using a sulfur atom as a 'stitch' to restrict the conformations and reactivity of intermediates. Coupling of p-cresol and p-bromotoluene to yield bis(p-tolyl) ether followed by sulfuration, oxidn., and bromination yields the brominated phenoxathiins II (R = Br2CH, BrCH2; R1 = Br2Ch, BrCH2, Me). II (R = R1 = Br2CH) undergoes silver nitrate-mediated hydrolysis, condensation with nitromethane, and redn. of the bis(nitroethenyl)dioxophenoxathiin with diisobutylaluminum hydride to yield bis(aminoethyl)phenoxathiin III; III is also prepd. by substitution of II (R = R1 = BrCH2) with potassium cyanide and redn. of the nitrile moieties with diisobutylaluminum hydride. Formylation of III and Bischler-Napieralski cyclocondensation yields I in addn. to two minor regioisomers. Using either addn. reactions of benzylmagnesium chlorides to I or redn. of I to an octahydrooxathiadiazapentacene followed by acylation, regioselective lithiation and alkylation with benzylic chlorides, complex mixts. contg. the desired dibenzyloxathiadiazapentacenes are obtained. Alkylation reactions of benzyl halides with acyltetrahydroisoquinolines and addn. reactions of benzylic Grignard reagents to dihydroisoquinolines are performed. A bis(pivaloyldihydroisoquinolinylmethyl)phenyl ether IV is prepd. from N-pivaloyl-1,2,3,4-tetrahydroisoquinoline and 4-[3-(bromomethyl)phenoxy]benzyl bromide (V) (prepd. in three steps from 4-bromobenzaldehyde and 3-hydroxybenzaldehyde); attempts to couple V to an octahydrooxathiadiazapentacene by lithiation and alkylation fail.