Enantioselective synthesis of an oxa-taxane derivative via tandem intramolecular [2+2] cycloaddition and [3,3]-sigmatropic rearrangement of allenyl ether

Tandem Reactions Combining Diels-Alder Reactions with Sigmatropic Rearrangement Processes and their Use in Synthesis

“…Using optically pure Wieland-Miescher ketone as starting material the propargyl ether 65 could be obtained in high optical purity (Scheme 21). 62 Treating the propargyl ether 65 with potassium tert-butanolate in tert-butanol triggered the described sequence of events finally leading to an oxa-taxane derivative 66 in excellent yield and high optical purity. 63 To be able to execute the tandem process using the nitrones 65a-b it proved necessary to use the 2,4-dinitro-phenylsulfinylpropadiene 66.…”

Enzymatic Baeyer–Villiger Oxidation of Bicyclic Diketones

“…Compounds (4aR,5S)-3 and (4aR,5R)-4 were confirmed by comparison with authentic samples. [13] Chemical Oxidation of Wieland-Miescher Ketone (1) The Wieland-Miescher ketone (1; 70 mg, 0.39 mmol) was magnetically stirred at room temperature in dichloromethane (7.8 mL) containing mCPBA (406 mg, 1.18 mmol). The reaction was stopped after 48 hours and worked up.…”

“…Actually, the incubation of (R)-1 with a crude preparation of CHMO gave a small amount of alcohols (4aR,5S)-3 and (4aR,5R)-4 identified by comparison with authentic samples obtained via NaBH 4 reduction. [13] The formation of the two alcohols 3 and 4 was due to a contaminating dehydrogenase activity, present in the crude preparation of CHMO, which came from the E. coli strain where the enzyme was overexpressed. [11] In fact, when rac-1 was treated with a crude preparation obtained from the same E. coli strain, but that did not contain the CHMO gene, only the alcohols were formed in small amounts.…”

Biocatalytic Approaches to the Enantiomers of Wieland–Miescher Ketone and its Derivatives

“…The unselective reduction of the C 1 carbonyl moiety of 1 should theoretically afford a complex mixture of stereoisomeric alcohols (5‐hydroxy‐4a‐methyl‐4,4a,5,6,7,8‐hexahydronaphthal‐en‐2(3H)‐one) which exist as two couples of cis ‐ and trans ‐enantiomers (compounds (4a S , 5 S )‐ 2 a , (4a R , 5 R )‐ 2 b and (4a S , 5 R )‐ 3 a , (4a R , 5 S )‐ 3 b in Scheme 1). These chiral derivatives, when obtained as enantiomerically enriched species, are known to be important building blocks for the synthesis of natural, bioactive products or compounds of pharmaceutical interest [13–17] . The presence of an enone group, in fact, easily allows to further manipulate their molecular skeleton and to transform them into structurally complex compounds.…”

“…These chiral derivatives, when obtained as enantiomerically enriched species, are known to be important building blocks for the synthesis of natural, bioactive products or compounds of pharmaceutical interest. [13][14][15][16][17] The presence of an enone group, in fact, easily allows to further manipulate their molecular skeleton and to transform them into structurally complex compounds.…”