Inversions Mitsunobu inversion

The stereoselective allylic rearrangement of the allylic alcohol 798 catalyzed by PdCl2(MeCN)2 and Ph3P under Mitsunobu inversion conditions is explained as proceeding via a rr-allylpalladium intermediate[496]. The smooth rearrangement of the allylic p-tolylsulfone 799 via a rr-allylpalladium intermediate is catalyzed by a Pd(0) catalyst[497]. 

Within the diastereomeric switch sequences, the corresponding trans-diols become accessible either using a Mitsunobu inversion or a reversible Diels-Alder cyclization as key reaction step [249,250]. This synthetic strategy is complementary to an approach involving metabolic engineering of E. coli via the chorismate/ isochorismate pathway [251]. 

Carboxylate anions derived from somewhat stronger acids, such as p-nilrobcnzoic acid and chloroacetic acid, seem to be particularly useful in this Mitsunobu inversion reaction.53 Inversion can also be carried out on sulfonate esters using cesium carboxy-lates and DMAP as a catalyst in toluene.54 The effect of the DMAP seems to involve complexation and solubilization of the cesium salts. 

The sequence detailed here provides 3-(S)-((tert-butyldiphenylsilyl)oxy)-2-butanone in high purity and on a preparative scale from inexpensive (S)-ethyl lactate. This optically active ketone should be a useful intermediate for the preparation of a variety of enantiomerically pure materials. It has been used in our laboratory for an asymmetric synthesis of (+)-muscarine3 and in the preparation of various other optically active tetrahydrofurans.4 Mitsunobu inversion of (S)-ethyl lactate followed by protection to provide 2-(R)-((tert-butyldiphenylsilyl)oxy)propanoate5 affords, by this method, ready access to the enantiomer of the title compound. 

The Mitsunobu reaction offers a powerful stereochemical transformation. This reaction is very efficient for inverting the configuration of chiral secondary alcohols since a clean SN2 process is generally observed ( Mitsunobu inversion ). Considering the fact that Mitsunobu chemistry is typically carried out at or below room temperature, high-temperature Mitsunobu reactions performed under microwave con-... 

Jin and Weinreb reported the enantioselective total synthesis of 5,11-methano-morphanthridine Amaryllidaceae alkaloids via ethynylation of a chiral aldehyde followed by allenylsilane cyclization (Scheme 4.6) [10]. Addition of ethynylmagnesium bromide to 27 produced a 2 1 mixture of (S)- and (R)-propargyl alcohols 28. Both of these isomers were separately converted into the desired same acetate 28 by acetylation or Mitsunobu inversion reaction. After the reaction of 28 with a silyl cuprate, the resulting allene 29 was then converted into (-)-coccinine 31 via an allenylsilane cyclization. 

The ready availability of the selectively protected 2,4,5-trihydroxypentanoic acid derivatives of defined stereochemistry, such as (2S,4S)-2,4,5-trihydroxypentanoic acid 4,5-acetonide methyl ester described here, coupled with Mitsunobu inversion,3 7 provide chiral synthons with the promise of broad utility. 

The same basic strategy was applied to the synthesis of the smaller fragment benzyl ester 28 as well (Scheme 4). In this case, aldehyde 22 prepared from (S)-2-hydroxypentanoic acid [9] was allylated with ent-10 and tin(IV) chloride, and the resulting alcohol 23 was converted to epimer 24 via Mitsunobu inversion prior to phenylselenenyl-induced tetrahydrofuran formation. Reductive cleavage of the phenylselanyl group, hydrogenolysis of the benzyl ether, oxidation, carboxylate benzylation, and desilylation then furnished ester 28. 

Treatment of the /3-keto ester 220 with sodium ethoxide at elevated temperature triggered off an epoxide ring opening by / -elimination that was followed by the desired Knoevenagel condensation to afford the tricyclic product 206 (Scheme 34). The enone moiety in the intermediate 221 did not show a propensity for deprotonation and, therefore, the ketone carbonyl function of the enone moiety was available for a Knoevenagel condensation. The reduction of the p-keto ester (206) to the corresponding diol was the next objective. Treatment of the TES-protected -keto ester (TES-206) with DIBAH afforded the diastereomeric diols 222 and 223 in a moderate diastereoselec-tivity in favour of the undesired diastereomer 222. The diastereomers were separated and the undesired diastereomer 222 was epimerized to 223 by a sequence that consists of Mitsunobu inversion and benzoate ester reduction [98, 99]. 

Both intermediates 43a and 43b were converted to the final molecule duloxetine (3), as described in Scheme 14.11. Therefore, route A involved direct transformation of the (5)-chloroalcohol 43a into the corresponding iodide, followed by amination and etherification. In contrast, route B consisted of Mitsunobu inversion of (R)-chloroalcohol 43b... 

Benzyl -o-xylopyranoside was converted into the alcohol 54 (a somewhat capricious isopropylidenation) [39] and a Mitsunobu inversion with N-hydroxyphthalimide, followed by protecting group removal, gave the hydro-xylamine 55. Transfer-hydrogenation (ammonium formate and palladium-on-charcoal in refluxing methanol) [40] then gave, on a small scale and in almost a quantitative yield, the enantiomer of the desired tetrahydro-l,2-oxazine 52. We have never been able to repeat this result since Figure 4 shows the NMR spectra acquired at the time [41]. 

Scheme 4.30 Combined kinetic resolution and Mitsunobu inversion.

Thus, 1.7-octadiene (79), which was subjected to monohydroboration followed by asymmetric dihydroxylation of the remaining double bond to give triol 80 with approximately 80% ee. Further transformations then afforded the desired butenolide 81. Double asymmetric dihydroxylation of diene 83 and subsequent protection gave hydroxy lactone 84 [98], which was then converted into acetylenic bis(hydroxy)bistetrahydrofuran 82 as the required intermediate for the (+)-asimicin synthesis. Mitsunobu inversion at C-24 gave rise to the diastereomeric (+)-bullatacin precursor. 

Not surprisingly, an attempt at direct Mitsunobu inversion of (3-hydroxyketone 14 led only to elimination, yielding the corresponding a,(3-unsaturated ketone. To circumvent this problem, 14 was converted to homoallylic alcohol 15 by Petasis methylenation via the corresponding TES ether. Attempts to methylenate (3-hydroxyketone 14 directly under Petasis conditions led to substantial decomposition via elimination and retro-aldol pathways. Alcohol 15 underwent smooth Mitsunobu inversion to give, following methanolysis and TES ether formation, the desired 1,4-anti compound 16 (Scheme 3). This was then converted in three straightforward steps to aldehyde 17, ready for the proposed aldol union with ketone 10. 

Lactone inversion.3 The rran.v-y-lactone 1 has been converted into the cis-isomer (2) by treatment of the dry potassium salt of the hydroxy acid derived from 1 with sulfene, followed by relactonization. The Mitsunobu inversion failed in this case. 

Tosylation with inversion.1 The reaction of a secondary alcohol with zinc tosylate, diethyl azodicarboxylate, and triphenylphosphine (Mitsunobu inversion, 5, 728) leads to the inverted tosylate in about 80-95% yield. Lithium tosylate is less effective. The reaction is sensitive to steric hindrance. 

For example, the fermentation of (2-bromoethyl)-benzene with recombinant E. coli furnished excellent yields of the corresponding c/.v-diol. enantiopure 3-(2-bromoethyl)-benzene-l,2-diol. The latter was used as a building block in the total synthesis of (+)-codeine (Fig. 29). Besides a Mitsunobu inversion of one of the stereogenic centers, two successive Heck cyclizations led to the enantiomer of the natural product [173]. Slight modifications of the reaction sequence, generating an epoxide intermediate, also furnished access to the naturally occurring enantiomer (—)-codeine [28]. 

Dodge, J. A. Nissen, J. S. Presnell, M. A general procedure for Mitsunobu inversion of sterically hindered alcohols inversion of menthol. (lS,2S,5R)-5-Methyl-2-(l-methyl-ethyl) cyclohexyl 4-nitrobenzoate. Org. Synth. 1998, Coll. Vol. IX, 607-609. 

As expected, Mitsunobu inversion of the allyl alcohol22 using HN3 gave predominantly the a-azide 23 (72). Mild hydrogenation of 23 with 1 atm of hydrogen over Raney Ni produced the corresponding amino compound 24 in a quantitative yield without any significant reduction of the olefin. 

On one hand, the a,P-unsaturated lactone 40, which was derived from di-O-acetyl-L-rhamnal (39) according to reported procedures, was submitted to Mitsunobu inversion with HCO2H, followed by hydrolysis and methoxymethylation to afford 40. On the other hand, the o-methylbenzoate 41 was obtained from 3,5-dihydroxytoluene under the protocols described by Solladig. 

Fig. 2.33. Mitsunobu inversion a typical substrate, the reagents, and products (possible preparation of the substrate Figure 2.27). "DEAD" stands for diethyl-azodicarboxylate.

If the Mitsunobu inversion is carried out intramolecularly (i.e., in a hydroxycarboxylic acid), a lactone is produced with inversion of the configuration at the OH-bearing stereocenter (Figure 2.35). This lactonization is stereochemically complementary to the paths via activated hydroxycarboxylic acids, which lead to lactones with retention of the configuration at the OH-bearing C atom (Section 6.4.2). 

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