Protective groups reductive, total

In addition to these studies, the Harmata group also successfully achieved the total synthesis (+)-curcumene 208 and curcuphenol 209 utilizing the 2,1-benzothiazine chemistry <03TL7261>. The synthesis of (+)-curcuphenol was accomplished by reduction of benzothiazine 94, followed by protection, desulfurization, reductive deamination and deprotection to give diol 223 in good yield. The latter was then converted into (+)-curcuphenol 209 (Scheme 63). The total synthesis of (+)-curcumene involved a similar approach to that of (+)-cucurphenol. 

To date, two total syntheses of myriaporone 4 are known. This chapter is based on the total synthesis of myriaporone 4 published by Taylor et al. in 2004. The synthesis of a chiral precursor, which has also been employed for the total synthesis of related compounds, was published by the same group in 1998. The linear total synthesis starts with an enantiomerically pure molecule from the chiral pool that delivers the stereogenic center at C-12 of the final product, employs Evans aldol reactions as key steps for stereoselective chain elongations and additionally includes reduction/oxidation steps as well as protecting group chemistry. 

Synthesis from L-threitol The L-threitol derivative 24, obtained from D-(-)-diethyl tartarate in three steps and 90% overall yield, was used as a starting material for the synthesis of nectrisine (1) (Scheme 5). " Swern oxidation of 24 produced the L-threose derivative 25, which was transformed into the aminonitrile 26 in 96% overall yield from 24, as an inseparable diastereomeric mixture. Removal of the silyl protecting group from 26 followed by oxidation of the resulting primary hydroxyl group with TPAP afforded the lactam 27, which was treated with sodium methoxide to produce the methyl ester 28 in 62% yield from 26. Lithium borohydride reduction of 28 afforded a chromatographically separable mixture of the lactams 29 and 30 in a ratio of 56 44 and 87% total yield. Silylation... 

The next steps in the synthesis include the multistep conversion of E)-15 into 16, subsequent cleavage of the silyl ether protecting group, and cyclization of 17, which cannot be isolated, to provide hexacyclic 18. With the reductive removal of the sulfonamide Magnus et al. arrived at their first goal, the total synthesis of the Wieland-Gumlich aldehyde (2). The conclusion of the total synthesis of strychnine is also within reach the authors succeed in converting 2 into the natural prod-... 

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