Preparative methodology and pyrolytic behavior of anthrylmonocarbenes: Synthesis and chemistry of 1H-cyclobuta[de]anthracene

This study involves (1) the behavior of organolithium reagents (1-6), (2) d evelopment of efficient methods for preparing 9(7)- and 1(8)-[methoxy(trime thylsilyl)methyl] anthracenes and their analogues, (3) the intramolecular c hemistry of the 9(9)- and 1(l0)-anthrylcarbenes generated by pyrolyses of 7 and 8, respectively, and (4) investigation of thermal behavior and bromina tion of the 1H-cyclobuta[de]anthracene (11) obtained from 9 or 10. alpha-Me thoxy-9-anthrylmethyllithium (1), prepared from 9-(methoxymethyl)anthracene (14) and t-BuLi in TMEDA/Et2O/pentane, reacts at C-10 with D2O, chlorotrim ethylsilane, dimethyl sulfate, benzoyl chloride, acetaldehyde, benzaldehyde , and acetone to give, after neutralization, 9,10-dihydro-9-(methoxymethyle ne)-10-substituted- anthracenes 15 and 21a-f. However, lithiation of 9-(thi omethoxymethyl)anthracene (25) with t-BuLi/TMEDA/Et2O/pentane occurs by an apparent radical-anion displacement process to give 9-anthrylmethyllithium (3), which then reacts with chlorotrimethylsilane to yield 9-(trimethylsily lmethyl)anthracene (28). Similarly, 28 is formed from 25 and from 9-(trimet hylsilyloxymethyl)-anthracene (29) with lithium and then chlorotrimethylsil ane. The electrophiles D2O, dimethyl sulfate, and benzaldehyde react with 3 at its methyl and its C-10 positions. [Methoxy(trimethylsilyl)methyl]arene s 40-42 and 7 are obtained by reactions of their aryllithium and arylmagnes ium bromide precursors with bromo(methoxy)methyltrimethylsilane (39). 1-(Me thoxymethyl)anthracene (45) is converted conveniently by t-BuLi and chlorot rimethylsilane to 8. Flash-vacuum pyrolyses of 7 and 8 yield 11 preparative ly; 11 then thermolyzes to 2H-cyclopenta[jk]fluorene (46). Decomposition of 9-deuterio-10-[methoxy(trimethylsilyl)methyl]anthracene (55) at 650 degree s C/10(-3) mm results in 10(56)- and 1(57)-deuteriocyclobutanthracenes, thu s revealing that the 10-deuterio-9-anthrylcarbene inserts to give 56 and al so isomerizes extensively before yielding 57. Of note is that 56 isomerizes thermally by C-10-D movement to form 2-deuteriocyclopentafluorene 58, 57 r earranges by Clo-H movement to yield deuteriocyclopentafluorene 59, and 58 and 59 equilibrate 1,5-sigmatropically. Possible mechanisms for the isomeri zations of 56 and 57 are outlined. Further, bromine adds rapidly to 11 to f orm 9,10-dibromo-9,10-dihydro-1H-cyclobuta[de]anthracene (94), which elimin ates HBr on warming to yield 10-bromo-1H-cyclobuta[de]anthracene (95).