SiPhos

Aristolochic Acid. Rosenmund and Reichstein prepared their material from roots and rhizomes of A. Sipho. It has the formula Cj HjiO N, m.p. 275° (dec.), and forms a methyl ester, m.p. 280° (dec.), [a]n 0°, which is difficult to saponify and on. hydrogenation gives a bright yellow substance, m.p. 312°, which forms a diacetyl... 

Zhou et al. have reported extensively on the use of a spiro-biindanediol as the backbone in the ligands 35a-f (Scheme 28.11, SIPHOS) [70]. Excellent results are obtained for a variety of substrates, and recently a full report has appeared on the use of these ligands [71]. Synthesis of the diol backbone requires a number of steps, including a resolution [72]. An additional and successful spiro-diol-derived phosphoramidite 39 has recently been disclosed by the group of Zhang [73]. 

The methyl-substituted substrate has been hydrogenated with SIPHOS in excellent ee see Ref. [68b],... 

The biosynthesis of aristolochic acids is considered to begin with 1-ben-zyltetrahydroisoquinoline precursors and to proceed via aporphine intermediates (5). In radioactive labeling studies, Spenser and Tiwari infused d/-tyrosine-2- C into the stem of A. sipho. The C-labeled aristolochic acid I formed lost more than 60% of its radioactivity when it was decarboxylated to the corresponding nitro phenanthrene derivative. Administration of d/-dihydroxyphenylalanine-2- C re-... 

The results in Table 14.8 show that very high enantioselectivities can be obtained using the diethyl39 or piperidinyl40 MonoPhos ligands or with any member of the SIPHOS family.36a c... 

Fig. 71.—Portion of cross-section of four-year-old stem of Aristolochia sipho, as shown by the rings of growth in the wood. The letters are the same as in Pig. 68 but new tissues have been added by the activity of the cambium and a cork cambium has arisen from the outermost collenchyma cells and given rise to cork. The new tissues are I, cork cambium k, cork g, secondary phloem from the cambium, and just outside this is older crushed phloem , secondary xylem produced by the cambium m, secondary medullary ray made by the cambium (notice that this does not extend to the pith). Half of the pith is shown. Notice how it has been crushed almost out of existence. Compare Figs. 68 and 71, tissue for tissue, to find out what changes the primary tissues undergo with age, and to what extent new tissues are added. Photomicrograph x 20. (From Stevens.)...

Craig, A.K., Dobkin, S., Grimm, R.B. and Davidson, J.B., 1969. The gastropod, Sipho-naria pectinata a factor in destruction of beach rock. Am. Zool., 9 895—901. 

In 2002, Zhou and coworkers designed and synthesized a new type of spiro phosphoamidites 1 based on spirobiindane backbone [20]. These spiro monopho sphoramidite ligands 1, especially SIPHOS (la), showed high enantioselectivities (up to 99.7% ee) in the rhodium catalyzed asymmetric hydrogenation of arylenamides (Scheme 8.4) [15]. The reaction was performed under typical conditions with rhodium catalyst, usually produced in situ from [Rh(COD)2 BP.i with 2 equiv of... 

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