Bridged Ring Systems by Anionic Rearrangement¹

Abstract

in bis(2-ethoxyethyl) ether l 5 to the tetracyclic hydrocarbon 14 (C9Hlz, t~~j~1 . 4 9 2 8, v 3067-3055 cm.-l) identical with the product obtained by Wolff-Kishner reduction of the known ketone 15. l6 (15) L. Friedman and H . Shechter, J . Am. Chem. Soc., 81,5512 (1959); 83, 3159 (1961). (16) H. K. Hall, Jr., J . Org. Chem., 25, 42 (1960). We are grateful to Dr. Hall, who kindly furnished a sample of 15 to facilitate identification with material we prepared by independent routes. Bridged Ring Systems by Anionic Rearrangement Sir :The propensity of bridged-ring molecules to undergo carbonium ion rearrangements is well appreciated. Recent evidence for the existence of homoenolate ions3 led us to explore the possibility that skeletal rearrangements via such anions might afford direct routes to systems otherwise difficultly obtainable. We now demonstrate the potential usefulness of this approach by applying it to the synthesis of tricycl0[4.2.1.0~~~]nonan-2-one (3). This skeleton along with other bridged systems presented here is of inherent interest in studies of carbonium ions and carbanions.j Treatment of brexan-2-one (1)j with potassium t-butoxide in t-butyl alcohol at 185' for 150 hr. transformed it (ca. 60% yield) into an isomeric ketone, CgH120 (m.p. 118.5-119.5", v 1747CgH120 (m.p. 118.5-119.5", v , 1169CgH120 (m.p. 118.5-119.5", v , and 1022 semicarbazone, C10HljN30, m.p. 159.5-162°).6 The following interconversions established the structure of this isomer as 3. The sodium salt of 5-norborneneendo-2-carboxylic acid (7a)' was converted to its acid chloride (7b) (v 1801 cm.-') with oxalyl chloride and then directly to the liquid diazoketone 7c (v 3062, 2005, and 1633 cm.-') by treatment with diazomethane. Without purification, the diazoketone was heated with copper powder in tetrahydrofuran8 and afforded the tetracyclic ketone 4 (CgHloO, m.p. 90.5-92', v 3045 and 1731 cm.-', X (95% ethanol) 271 mp ( E 50),9 no olefinic protons by n.m.r. ; semicarbazone, Cl0Hl3N30, m.p. 204-205 " ; 2,4-dinitrophenylhydrazone, C15H14N404, m.p. 210-21 1 ').Hydrogenation of 4 with palladium in ethyl acetate cleaved a cyclopropyl bondlo and gave a tricyclic ketone shown to be 5 (CsH120, m.p. 120-

Carbon‐13 NMR Studies. 127—13C and 2H NMR investigations of 1H/2H exchange in isomeric tricyclic [5.2.1.0] and [5.3.1.0] ketones

“…Attenuation of the rate of p-enolization at C-6 in 7 is also apparent relative to 1 but the usual preference for exo-proton abstraction is evident. Similar regioselectivity of pexchange at the methyl groups were observed, favoring exo-methyl exchange as has been observed in all cases to date.2,'6,'7 Stereoselective syn-exchange at C-1 1 in 6 and 8 is consistent with the notion that steric hindrance plays a role in the process but, as noted above, this is condition^.^ The p-enolate rearrangment of 1 + 2 proceeds about twice as fast as the rearrangement of 6, 3.2 x lop6 s-' vs 1.6 x lop6 s-', and the latter is nearly an order of magnitude faster than syn-11 exchange in 6. Perhaps syn-exchange at the methano bridges in 3, 5, 6 , 8 and 9-11 proceeds through an intermediate species which differs from that involved in the rearrangements of 6 and 8.…”

Nuclear Magnetic Resonance Studies. XXVII. Homoenolization of Fenchone. A Mechanistic Study Utilizing C And H Nuclear Magnetic Resonance

“…The synthetic potential of skeletal rearrangement via homoenolate anions to generate systems otherwise difficult to obtain was also demonstrated in the initial investigations of homoenolization by Nickon et al (4). Treatment of brexan-2-one (4) with t-BuO--t-BuOH at 185" gave a 60% yield of brendan-2-one (5).…”

Bicyclooctanone Rearrangement, [3.2.1] → [3.3.0], via β-Enolization. Evidence for γ-Enolization in Bicyclo[3.3.0]octan-2-one

“…Nevertheless the process has synthetic utility (2) and warrants further investigation to define its scope more precisely in terms of suitable molecular geometries and the stereochemistry of ketonization. At present these features are established only for the bicyclo[2.2.1]heptan-2-one skeleton (1,3) and adamantanone (4) 4While hornoenolization neatly describes the process at fi carbons, more remote proton abstraction can occur.…”