Acorenones

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... 

Copper catalysed decomposition of diazoketone 41 furnishes tricyclic ketone 42 in 83% yield (equation 52) which provides the key building block in the synthesis of chysomelidi-al81. A few similar instances of cyclopropanation are to be found in the syntheses of ( )-hinesol 4382, (-)-acorenone B 44, ( )-spirolaurenone 45s4 and (t)-descarboxyquadrone 4685 (equations 53-56). 

This process has been coupled with meta addition of a carbonyl anion equivalent and the controlled exo addition of the incoming nucleophile to generate acorenone and acorenone B stereospecifically from [(o-methylanisole)Cr(CO)3] (63 Scheme 14).123 The first step is addition of a cyanohydrin acetal anion (64) to the less-hindered meta position in [(o-methylanisole)Cr(CO)3]. Addition of allylMgBr to the resulting ketone, anti-Markovnikov addition of HBr to the alkene, substitution for Br by CN, and coordina-... 

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... 

A new stereocontrolled synthetic route to acorenone-B (108) (c/. Vol. 6, p. 62) has been developed by using a combination of spiroannelation, secoalkylation, and... 

Examples of two types of 1,2-alkylative carbonyl transpositions occur in Corey s occidentalol synthesis19), and in Oppolzer s acorenone synthesis20). In the first,... 

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. 

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