Synthesis of peri-cyclobutarenes by thermolysis of [methoxy(trimethylsilyl)methyl]arenes

[Methoxy(trimethylsilyl)methyl]arenes are readily prepared by reactions of chlorotrimethylsilane with (alpha-methoxy)arenylmethyllithium reagents as obtained from (methoxymethyl)arenes and t-BuLi. The [methoxy(trimethylsilyl)methyl] arenes eliminate methoxytrimethylsilane at 525-675 degrees C/0.05-0.10 mm to yield peri-cyclobutarenes as derived from arenylcarbenes. Of importance is the fact that the initial arenylcarbenes generated insert into adjacent peri C-H bonds and/or isomerize to other arenylcarbenes that insert into their peri C-H bonds to give peri-cyclobutarenes. Thus, flash-vacuum pyrolysis of 1-[methoxy(trimethylsilyl)methyl]naphthalene (13) at 575-675 degrees C/0.05-0.10 mm yields 1H-cyclobuta[de]naphthalene (6, up to 39%) in practical quantities. 2-[Methoxy(trimethylsilyl)methyl]naphthalene (23) also affords 6 as a major thermolysis product. At 510 degrees C/ 0.05-0.10 mm 4-methoxy-1-[methoxy(trimethylsilyl)methyl]naphthalene (29) decomposes to 4-methoxy-1H-cyclobuta[de]naphthalene (31, 46%). Under similar conditions, 2-methoxy-1-[methoxy(trimethylsilyl)methyl]naphthalene (33) converts to 1,2-dihyrdronaphtho[2,1-b]furan (35, 64%) and naphtho[2,1-b]furan (36, 31%), presumably by insertion of 2-methoxy-1-naphthylcarbene (34) into a C-H bond of its o-methoxy group and then dehydrogenation of the resultant dihydrofuran. Further, 1-[methoxy(trimethylsilyl)methyl]-6-methylnaphthalene (39) pyrolyzes (510 degrees C/0.10-0.20 mm) to 6-methyl-1-naphthylcarbene (40), which isomerizes in part to 7-methyl-1-naphthylcarbene (49); carbenes 40 and 49 then undergo peri C-H insertion to give 3-methyl-1H-cyclobuta[de]naphthalene (41) and 2-methyl-1H-cyclobuta[de]naphthalene (42) in an 8:1 ratio and a combined yield of 44%. The pyrolytic method is particularly valuable for preparing higher peri single carbon atom bridged arenes such as 4H-cyclobuta[jk]phenanthrene (53, 65%) and 3H-cyclobuta[cd]pyrene (59, 86%).