Homoenolate anions and homoenolate anion equivalents

1985

The behavior of the exo and endo isomers of 7,7-dimethyltricyclo[3.3.1.02,4]nonan-6-one (5, 6) under strongly basic conditions (t-BuOH/t-BuOH/185 °C) has been examined. In sharp contrast to their [3.2.1.02,4] analogs, the endo isomer is stable while the exo readily rearranges to 8,8-dimethyltricyclo-[4.3.0.02,4]nonan-7-one (16). Experiments were carried out in tert-butyl alcohol-O-d1 to establish the sites of deuterium incorporation in the initial ketones as well as the relative rates and stereoselectivities of the exchange processes. Ketones 5 and 6 were prepared through ring expansion by ketonization of cyclopropoxides generated from the [3.2.1.0] homologs; the stereochemistry of these ketonizations was established by 2H labelling.

Section: Otms Otmsmentioning

confidence: 86%

Section: Introductionmentioning

confidence: 99%

¹³C nuclear magnetic resonance studies. 114. An examination of the [3.3.1.0] → [4.3.0.0] rearrangement via β-enolization and H/D exchange in tricyclic ketones

Ragauskas¹,

1985

“…1 (Table 1) gave rise to a "C spectrum consistent with structure 20 (see text) while the major component from Expt. 3 exhibited a "C spectrum readily attributable to 21 as discussed in the text. These structural assignments were confirmed by unequivocal identification of their homoketonization products.…”

Section: Cyclopropanation Of 19mentioning

confidence: 85%

“…A second feature of the homoketonization process concerns the stereoselectivity of protonation of the homoenolate which, in general, is found to be high (3). However, in the case of p-enolates, high degrees of retention and inversion of configuration have been observed and definitive interpretation in terms of the principal governing factor is difficult.…”

Section: Introductionmentioning

confidence: 99%

¹³C magnetic resonance studies. 119. Tricyclo[3.3.0.0] and [3.2.1.0]octanones from substituted norbornenones via cyclopropanation and homoketonization

Ragauskas¹,

1985

ARTHUR J. RAGAUSKAS and J. B. STOTHERS. Can. J. Chem. 63, 2961 (1 985). Simmons-Smith cyclopropanation of the trirnethylsilyl enol ethers of 7-isopropylidene-and two 7-spirocyclopropylnorbornenones leads directly to the 8-substituted 2-trimethylsilyl ethers of hornoquadricyclene. Homoketonization of the unsaturated ether proceeds regiospecifically to the corresponding tricyclo[3.3.0.02~H]octan-4-one while the others give the tricyclo[3.2.1 .02.6]octan-4-ones exclusively, all with high stereoselectivity favoring inversion of configuration. This difference in the regiochemistry of homoketonization can be attributed to a directive effect of P-functionalization overcoming thermodynamic control of cleavage. ARTHUR J. RAGAUSKAS et J. B. STOTHERS. Can. J. Chem. 63, 2961 (1985). La reaction de cyclopropanation suivant Simmons-Smith des Cthers Cnoliques trimCthylesilyles de l'isopropylidene-7 et de deux spiro-7,cyclopropylnorbornCnones conduit directement aux Cthers trimCthylsily1-2 de I'homoquadricyclene substitues en position 8. L'homocCtonisation de 1'Cther insaturC est rCgiospCcifique et conduit a la tricyclo[3.3.0.02~x]octanone-4 correspondante tandis que les autres Cthers conduisent exclusivement aux tricyclo[3.2.1 .02'6]octanones-4; toutes ces reactions se produisent avec une tres haute stCrCosClectivitC qui favorise une inversion de configuration. On attribue la diffkrence de rCgiochimie dans I'homocttonisation a un effet directif de la fonction en P qui est plus puissant que le contr6le thermodynamique du clivage.[Traduit par le journal]

“…It is significant that, in either case, cleavage b must occur with retention of configuration at the carbon picking up the proton (C-l in the original skeleton). Although the majority of examples of p-enolate cleavage, for which the stereochemistry has been examined, proceed primarily with inversion of configuration, there are some systems which exhibit a high degree of retention (13). In the present cases of 15 and 16, inversion of configuration for cleavage via b would lead to a trans ring junction in the resulting ketones, each of which is a substituted 13.3.0) system.…”

Section: L]octan-2-onementioning

confidence: 87%

A new route to the cis–anti–cis triquinane ring system. The synthesis of 4,4-dimethyltricyclo[6.3.0.0^2,6]undecan-3-one via β-enolate rearrangement

Patel¹,

1984

A synthesis of cis, anti, cis-4,4-dimethyltricyclo[6.3.0.0'6]undecan-3-one is described in which the key step is p-enolate rearrangement of 9,9-dimethyltricyclo[5.3.1 The discovery and characterization of several naturally occurring compounds having the linearly fused tricyclopentanoid ring system of cis, anti, cis-tricyclo[6.3.0.02~6]undecane, such as hirsutene ( I ) and coriolin ( 2 ) , have attracted considerable interest since many of these materials exhibit anti-tumor and (or) antibiotic activity (1). An array of synthetic routes to 1, 2 , and congeners has been described (2) including, from this laboratory (3), a sequence leading to 1 which utilizes a stereocontrolled p-enolate rearrangement for the generation of the ring system. The key step is the conversion of 3 -+ 42 via proton abstraction from C-11 in 3 with the stereochemistry of the subsequent rearrangement constrained to give the correct con-'part 110 in the series ' "mr studies; for Part 109 see ref.8. The required tricyclic ketone 6 was prepared from the known epoxide 7 (4) as outlined in Scheme 1. After heating 7 under reflux with lithium triethyl borohydride ("Super Hydride") in THF ( 3 , the product was oxidized with alkaline peroxide to furnish a 85 : 15 mixture of alcohols 8 and 9 which were separable by flash chromatography (6). Pyridine -chromic acid oxidation (7) of 8 furnished the corresponding ketone 10a in high yield. The generation of the homologous ketone 12 via cyclopropanation of the silyl en01 ether of 1Oa followed by homoketonization failed, in sharp contrast to the behavior of the isomeric l l a which is readily transformed to 14 by this route (8). Each of several attempts, under a variety of conditions, gave a complex mixture of unidentified products. As an alternative, the Tiffeneau -Demjanov ring expansion (9) was examined and found to be satisfactory although less efficient because of the concomitant formation of the unwanted isomer 13. Treatment of 10a with trimethylsilyl cyanide (10) gave the trimethylsilyl cyanohydrin ether l o b , which was reduced to the p-aminoalcohol 10c with lithium aluminium hydride. Reaction of 1Oc with nitrous acid furnished a 2: 1 mixture of ketones 12 and 13 which were separated by flash chromatography. The overall yield for the ring expansion of IOU -+ 12 and 13 was 80%. Ketones 12 and 13 were easily distinguished by their I3Cmr spectra since the quaternary carbon signals appeared at 66.1 and 52.6 ppm, respectively. The 13.5 ppm downfield shift of this signal in 12 is readily attributed to the a-carbonyl group. The identity of these ketones was confirmed by carrying alcohol 9 through the same series of reactions to a 64: 36 mixture of two ketones in 74% yield. These two ketones were separated 'With the skeletal rearrangement. a different numbering scheme is required as indicated in the formulas. Can. J. Chem. Downloaded from www.nrcresearchpress.com by 54.202.233.140 on 05/12/18For personal use only.