Aromatic Substitution and Addition Reactions of 1H-Cyclobutanaphthalenes

Article abstract of DOI:10.1021/jo00350a053

Nitration of 1H-cyclobutanaphthalene (1) with nitric in sulfuric and acetic acids or with acetyl nitrate yields 4-nitro-1H-cyclobutanaphthalene (6) and 4,5-dinitro-1H-cyclobutanaphthalene (8).Similarly, 1-bromo-1H-cyclobutanaphthalene (5) nitrates to 1-bromo-4-nitro-1H-cyclobutanaphthalene (10).Reaction of 1 and bromine in the presence of ferric bromide gives 4-bromo-1H-cyclobutanaphthalene (7) and 4,5-dibromo-1H-cyclobutanaphthalene (9).Reduction of 6 with aluminum amalgam in protic environments or by hydrogenation over palladium results in 4-amino-1H-cyclobutanaphthalene (11), diazotization of which with nitrous and hydrobromic acids yields 1H-cyclobutanaphthalene-4-diazonium bromide (12) and then 7 upon reaction with cuprous bromide. 4-Acetyl-1H-cyclobutanaphthalene (13) and 4-(phenylacetyl)-1H-cyclobutanaphthalene (14) are formed efficiently by Friedel-Crafts acylations of 1 with acetyl chloride and with phenylacetyl chloride.The present study thus reveals that (1) electrophilic substitution of 1 occurs regiospecifically at its C₄ position and (2) 1 does not undergo ring opening of its cyclobuta moiety during the above reactions.The rates of electrophilic bromination and acetylation of 1 relative to naphthalene (18), acenaphthene (19), and 2,3-dihydro-1H-phenalene (20) are 19 > 20 > 1 > 18; nitration of 1 also occurs more rapidly than that of 18. n-Butyllithium effects conversion of 7 to 4-lithio-1H-cyclobutanaphthalene (24) which isomerizes slowly to 1-lithio-1H-cyclobutanaphthalene (25).Addition of bromine to 1 takes place upon photolysis to give a tetrabromide assigned as 1aα,2β,3β,4α-tetrabromo-1a,2,3,4-tetrahydro-1H-cyclobutanaphthalene (3). 2,4-Dibromo-1H-cyclobutanaphthalene (35) is formed by dehydrobromination of 30 with DBU; Red-Al effects conversion of 30 to 1.Photobromination of 5 results in benzenoid addition to yield two pentabromides provisionally assigned as 1,1aα,2β,3α,4α-pentabromo-1a,2,3,4-tetrahydro-1H-cyclobutanaphthalene (37, major) and 1,1aα,2β,3β,4α-pentabromo-1a,2,3,4-tetrahydro-1H-cyclobutanaphthalene (38, minor).Reactions of 37 and 38 with Red-Al result in regeneration of 5.