Approaches to 1H‐Cyclopropa[l]phenanthrenes. Eliminations with 1a,9b‐Dihydro‐1H‐cyclopropa[l]phenanthrene Derivatives

Abstract

Base-induced elimination of the sulfonium salt 2i in the presence of furan affords the addition products 7 and 8, derived from 1H-cyclopropa[l]phenanthrene (1) and the isomeric cyclopropene 5a (Scheme 3). Upon oxidation, the selenide 2c yields phenanthrene-9-methanol (9), presumably via 1. No evidence for the intermediate 1 is obtained from sulfoxide pyrolysis with 2e, which leads to products formed by radical pathways (Scheme 5 ) . Reductive elimination of the disulfone 3b gives half-reduction to monosulfone 2g and complete reduction to cyclopropane 2 as well as 9methylphenanthrene (IS), but no evidence for the intermediate 1. Scheme I2 1 3 Substituted la,9b-Dihydro-lH-cyclopropa[l]phenanthrenes. -Compounds of structure 2 are in principle available via carbene addition to 9-substituted phenanthrenes [3] [6]. This approach was attempted, but abandoned when it was found impossible to effect dichlorocarbene addition to 9-bromophenanthrene under a variety of conditions. Similarly, the cyclopropan-forming procedure using diazomethane/CuBr which works for phenanthrene [7] afforded no addition product with the 9-bromo derivative. Alternatively, base-induced elimination of 1-halogenated dihydrocyclopropa[l]phenanthrenes in the presence of nucleophiles was investigated. Reaction of the dichlorocarbene adduct 4 [S] of phenanthrene with base in the presence of methanethiolate is known to afford the H E L~T I C A CHIMICA ACTA -Vol. 69 (1 986) Scheme 2 4 CI

ChemInform Abstract: From Dichlorocyclopropanes to Furans and Cyclopentadienes via Vinylcarbenes.

“…See [4]. -9-Methoxyphenanthrene (la), I,l-Dichloro-la,9h-dihydro-la-methoxy-1 H-cyclopropa[ 1Jphenanthrene (Za), Phenanthro[9,10-b]run (6a).…”

“…In connection with research directed towards synthesis of cyclopropa [l]phenanthrenes [4], we reacted the dichlorocarbene adduct 2a [5] of 9-methoxyphenanthrene (la) with strong base and isolated phenanthro [9,lO-b]furan (6a) in 80% yield [6]. The result was interpreted by the sequence shown in Scheme 1, which is formulated in analogy to known reactions of dichlorocarbene adducts of phenanthrene [7-91: elimination of HC1 from 2 leads to the chlorocyclopropene 3 which undergoes ring opening to the chlorovinylcarbene 4.…”

“…The corresponding resonances in the "C-NMR are found at 6 37.78 ( t ) and 57.47 ( 4 ) ppm. This corresponds to cis-addition of MeSH, which is the rule for such systems [4]. The spectral data of the known 3-phenyl isomer of 15 [13] were useful for establishing the structure.…”

“…Similarly, 9-(2-phenylethyl)phenanthrene (13c), prepared from 9-phenanthrenecarbaldehyde (12) via alcohol 13a and chloride 13b, when subjected to the same sequence, gave the 2-phenyl-substituted cyclopentadiene 15 in 44.5% yield, together with 55.5% of unreacted 14. The position of the t-BuO group in 20 was deduced by comparison of the 'H-NMR spectrum with spectra of other dihydro-1H-cyclopropa [l]phenanthrenes [4]. Attempts to prepare other heterocyclic molecules by this route were unsuccessful.…”

Developments in cycloproparene chemistry

“…When the corresponding dimethylselenonium tetrafluoroborate is allowed to react with fert-butoxide in the presence of furan, ylide 83 is formed, dimethyl selenide is ejected, and the adducts 87 (20%), 88 (13%), and 89 (7%) are isolated.67,68 Moreover, Muller has subsequently discovered that the sulfur ylide 84 behaves in a similar manner. 66 The isolation of 87-89 requires the intervention of both lH-cyclopropa[/] phenanthrene 85 and its laH-isomer 86. The fact that 87 and 88 form the major proportion of the product mixture is consistent with the predominant abstraction of the benzylic 9b-proton of 83 strained aromatic 85. In the absence of trapping agent no discrete hydrocarbon products are isolated.…”