Conjugate reduction natural products synthesis

The 3.8-nonadienoate 91, obtained by dimerization-carbonylation, has been converted into several natural products. The synthesis of brevicomin is described in Chapter 3, Section 2.3. Another royal jelly acid [2-decenedioic acid (149)] was prepared by cobalt carbonyl-catalyzed carbonylation of the terminal double bond, followed by isomerization of the double bond to the conjugated position to afford 149[122], Hexadecane-2,15-dione (150) can be prepared by Pd-catalyzed oxidation of the terminal double bond, hydrogenation of the internal double bond, and coupling by Kolbe electrolysis. Aldol condensation mediated by an organoaluminum reagent gave the unsaturated cyclic ketone 151 in 65% yield. Finally, the reduction of 151 afforded muscone (152)[123]. n-Octanol is produced commercially as described beforc[32]. 

In contrast to the conjugated system, the reactivity of hexahydro-isoxazolo[2,3-tf] pyridines has been the subject of considerably more attention, which can most certainly be attributed to its greater synthetic potential, as demonstrated by the synthesis of many complex natural products. However, most of the reactions reported since 1996 have been known for many years and the last decade was in fact characterized by their use in syntheses or optimization. After a brief survey of the thermal reactions, procedures involving the reductive cleavage of the N-O bond will be detailed. 

A one-pot cascade reductive amination, conjugate addition and lactamisation of keto acrylate 112 afforded fused piperidinodiazepinone 113 in good yield <07T7187> while lactamisation was the final step in the synthesis of tetracyclic diazepinone natural products sclerotigenin and (-)-circumdatin-F <07TL3243>. 

Martin s sulfurane has been used to prepare a variety of cyclopentenes for use in the total syntheses of complex natural products. Myers effectively employed the title reagent to prepare synthetic intermediates for use in his total synthesis of the neocarzinostatin chromophore.43 (For dehydrations to yield alkenes in the nine-membered ring of this compound, see Section 3.7.5.4.) One example is reaction of tertiary alcohol 86 to furnish alkene 87 in 93% yield. In Phillips s total synthesis of cylindramide A, he employed a conjugate addition-reduction-elimination sequence (88—>89) to generate the... 

The selective reduction of polyfunctional molecules is of continuous interest in organic synthesis, especially in the field of natural products. Tetracyclic systans like styrenoid ketones have been found to be attractive precursors for the synthesis of cardiac glycosides. When the styrenoid bond in the enone was hydrogenated over 10% Pd/C in ethanol, at 1 atm of hydrogen and room tanperature, the double hydrogenated saturated ketone was formed (Scheme 11). However, the conjugated double bond in the unsaturated ketone was selectively reduced when the reaction was performed in piperidine (Scheme 11). 

Conjugated dienes are the object of continuous attention in organic chemistry. These compounds are encountered in numerous natural products and find applications in many fundamental methodologies in synthesis (cycloaddition, metathesis, ene-reaction, oxidoreduction, or reductive aldolization for instance) (Eig. 1). In addition. 

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