Of -acorenone

This same concept applies to spiroannulations of six membered rings and is illustrated in a synthesis of acorenone B 155 as outlined in Scheme 547). The notion of alkylative carbonyl transposition permits the spiro enone 156 to become a logical intermediate. The standard analysis by a retro-aldol process translates the spiro ring system of acorenone B into a geminal alkylation problem as revealed by... 

The possibility of readily introducing a meta sidechain to an anisole has enabled design an unusual synthesis of acorenone [17]. 

Arene-chromium tricarbonyl complexes. Seinmelhack and Yamashita have used (he activating and meta-directing effect of the CKCO)3 group to obtain the spiro-[4.5]decenone system of acorenone (3) and acorenone B (4) from anisole. Treatment... 

Minato et have reported the isolation of acorenone (149) from Acorus calamus L. The physical properties (m.p., [ajp) which they ascribe to this compound are markedly different from two previous sets of data. Hydrogenation ofacorenone is reported to give isoacorone (150 R = Me, = H)andacorone (150 R = H, R = Me). Recently, Conia et al. have demonstrated that thermal cyclization (220 °C) of the appropriately substituted cyclohexanone (151) [derived from (-+- )-3-methylcyclohexanone] yielded four isomeric spiro-diketones closely related to the acorane skeleton. The intermediacy of the isopropylidene isomer (152) was indicated and from a detailed study of n.m.r. solvent shifts and c.d. spectra it was concluded that these four spiro-diketones can be represented as (153)—(156). 

These epoxides can be converted to vinyl siloxycyclopropanes m high yield by treatment with base and trimethylsilyl chloride. Transformations of these interesting intermediates (see Section VII) into various products are demonstrated in equation 103. Isolation of oxaspiropentanes is not required in a route to cyclobutanones which are formed by straightforward acid workup (equation 104) . These can either be expanded to y-butyrolactones by oxidation or to an enol ester by a-formylation and acid-induced fragmentation. The latter sequence has been utilized in a synthesis of acorenone... 

Previously it had been shown that low temperature irradiation of the enone (168) gave the tricyclic ketone (169) as the major product. It has now been reported99 that further photolysis of (169) at 0—5 °C promotes a Norrish type II process to give the ketone (170) which can be converted into a-acoradiene (171). Epimerization of the isopropenyl group in (170) can be achieved by silver nitrate, thus paving the way for a synthesis of acorenone B (172). Pertinent to these results is the finding... 

Several new synthetic routes to acorane sesquiterpenoids have been published during the past year cf. Vol. 8, p. 76). In the first of these routes spiroannulation of the pyrrolidine enamine (201) derived from cyclopentene aldehyde (200) provided an enone (202) which was subsequently converted into (-)-acorenone (203) (Scheme 19). In an alternative synthetic route,Robinson annulation of the aldehyde (204) with methyl vinyl ketone provided a spiro-ketone (205) which served as a common intermediate in the synthesis of (-)-acorenone (203) and (-)-acorenone-B (211) (Scheme 20) cf. Vol. 7 pp. 63, 64). To explain the conversion of (206) into (209), it has been suggested that the intermediate 1,2-borane borate (207) undergoes elimination followed by hydroboration. 

The products are the fused bi-cyclic ring system as a mixture of diene isomers, and the spirocychc system [29]. The product ratio is dependent on the length of the chain and on the reaction conditions. Kinetic conditions in the example shown favor the fused bi-cyclic product, whereas thermodynamic conditions deliver the spirocyclic system. This approach was subsequently applied in a rapid synthesis of acorenone and acorenone B (see Chap. 8) [30]. 

Scheme 1 Total synthesis of ( )-acorenone B (rac-7) according to Semmelhack...

The cleavage with hydrogen chloride was used in a synthesis of (—)-acorenone... 

A new strategy for the synthesis of spiro[4,5]decane sesquiterpenoids has been developed which relies upon the activating and meta-directing effects of the tricarbonylchromium group in 7r-anisoletricarbonylchromium complexes with cyano-stabilized nucleophiles. This new methodology is nicely illustrated in the synthesis of acorenone (175) and acorenone B (176), which combine both inter- and intra-molecular variants of the process (Scheme 21). 

The addition of carbanions on the complex [Cr(T] -o-methylanisole)(C0)3] (see Chap. 10) leads, after a second nucleophilic attack of the same type followed by decomplexation, to a spiranne precursor of acorenone. The methoxy substituent has a remarkable meta-directing effect. ... 

M.F. Semmelhack, A. Yamashita - Arene-Metal Complexes in Organic Synthesis, Synthesis of Acorenone and Acorenone B, J. Am. Chem. Soc. 102,5924,1980. 

Reactions that generate carbon-carbon bonds via the addition of a carbanion to an arene metal complex or to a hydro-arene complex are likely to join the ranks of those which are sufficiently powerful that a whole synthetic route can be built around their use. Thus Semmelhack and co-workers report a synthesis of acorenone B (84) in which the key step is the conversion of (82) to (83). ... 

The rearrangement of adducts of enol acetates derived from a-diketones has been reported. An interesting application of this principle was in a model study for the synthesis of acorenones (Scheme 14) in which the adduct (49) underwent rearrangement in base to (50) which was cleaved with lead tetra-acetate to generate the spirocyclic product (51). ... 

SCHEME 17.7. Substrate-controlled asymmetric s3mthesis of (+)-acorenone B 28 through a [2,3]-sigmatropic rearrangement-ring contraction of ylide 26. 

Kido F, Abiko T, Kato M. Spiroannulation by the [2,3]-sig-matropic rearrangement via the cyclic aUylsulfonium ylide. A stereoselective synthesis of (+)-acorenone B. J. Chem. Soc., Perkin Trans. 1 1992 (2) 229-233. 

---