Nezukone synthesis

Oxygenated dienes are exceptional substrates for vinylcarbenoids [78]. In order to avoid side-products derived from zwitterionic intermediates, nonpolar solvents are typically employed. A short synthesis of nezukone 57 highhghts the utiHty of the [3-1-4] cycloaddition for the synthesis of tropones (Scheme 14.4). The cycloaddition between the oxygenated butadiene 55 and 52 generates the cycloheptadiene 56 in 67% yield [78]. Treatment of 56 with Meli followed by acid-induced dehydration completes a very short synthesis of nezukone 57. 

The iron carbonyl-promoted [3 + 4] cycloaddition of bromo-ketones to. 1,3-dienes provides a convenient way, via 2-oxyallyIs, of synthesizing tropones and hence thujaplicins. The synthesis of nezukone (154 X = H)253 has been reported from a,a,a, a -tetrabromoacetone and 3-isopropylfuran. Similarly, from 2-isopropylfuran, /3-thujaplicin (154 X = OH) has been synthesized from the corresponding tropone by known methods, and a-thujaplicin synthesis requires isopropyl substitution in the ketone moiety.254 Karahanaenone (155) is a minor product from pyrolysis of the benzoate (156).149... 

The examples shown in Scheme 2 illustrate (a) a method for RsC— Br -> RzO or R3C—OH and (b) dialkyladve enone transposition as shown in essence in equation (2). The sequence R2CH—Cl R2CH—Sn -> R20 was crucial in a synthesis of the troponoid nezukone (1), as other methods of functionalizing the R2CH—Cl system in this ring failed (equation 3). The dialkylative enone transposition (equation 2) was illustrated by a short synthesis of dihydrojasmone (equation 4). ... 

Silver fluoroborate, AgBF4 [I, 1007, before Silver iododibenzoate]. Mol. wt. 194.70. Preparation.1 Silver oxide (1.0 g.) is dissolved in 45% fluoroboric acid (7.2 g.). Synthesis of a tropone.1 The natural tropone nezukone (4) has been synthesized by addition of dichlorocarbene (CHClj,-potassium r-butoxide) to l-isopropyl-4-methoxycyclohexadiene-1,4 (2), obtained by Birch reduction of the anisole (1). The resulting adduct (3) was treated with silver fluoroborate to give the tropone (4) in... 

Noyori has transformed 8-oxabicyclooctanones into various naturally-occurring troponoids by acid-induced cleavage of the oxygen bridge, followed by dehydration and oxidation [181]. Equation 122 shows the synthesis of nezukone... 

Use of oxygenated dienes, e.g., 26, leads to the formation of tropone derivatives such as 28. A similar reaction sequence has been applied in the synthesis of nezukone (30)864. 

The reaction of a,a,a, a -tetrabromoacetone, 3-isopropylfurane, and diiron nonacarbonyl was used as the first step in a synthesis of the tropone nezukone... 

This tropone synthesis was used for a short synthesis of nezukone (7) (equation I). 

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