Transformation to aldehyde

Hydroxymethylation of ketone (155) was followed by protection of the aliphatic hydroxy group (2-methoxypropyl ether) and addition of an a-benzyloxymethylene group at C-4. Acidic workup at the last stage of the reaction sequence produced (156). Its transformation to aldehyde (157) was carried out by successive treatment with methoxypropyl ether, acetic anhydride and pyridine, hydrochloric acid and methanol, and finally chromic acid, pyridine and hydrochloric acid. Dehydration of (157) led to the formation of (158) in 20% yield. Reagents other than the mentioned produced appreciable quantities of the cis A/B isomer. The butenolide (159) was finally synthesized by oxidation and hydrogenolysis. In order to complete the synthesis of triptolide it was necessary to introduce the... 

TosMIC can be efriciently alkylated with primary alkyl halides, isopropyl iodide and benzyl bromide both to the corresponding mono- or di-alkyl derivatives using NaH in DMSO or 40% aq. NaOH in and in the presence of Bu"4NI (Scheme 125). The resulting compounds have then been transformed to aldehydes and ketones, including cycloalkanones, and the method has been successfully applied to the synthesis of optically active 2-methylcyclobutanone from the chiral sulfonylmethyl isocyanide and 1,3-dibromobutane. ... 

Harries and Langheld were the first to show that, on oxidation with ozone, the primary alcoholic hydroxyl groups of the sugar derivatives are transformed to aldehyde groups. 

Compound 34 was transformed to vinyl iodide 38, which corresponds to the C9-C14 fragment of discodermolide. After protection and reduction (Dibal-H), 34 was transformed to aldehyde 37 which was then converted to the (Z)-vinyl iodide 38 by using the iodoethylphosphonium (EtPPhal) [46]. The overall yield for the preparation for vinyl iodide 38 from 34 is 35% (Scheme 8). 

The construction of the alkenyl side chain and the control of the C9, CIO and Cll stereogenic centers was achieved from (5)-(+)-methyl 3-hydroxy-2-methylpropionate 1. (Scheme 21) This compound was transformed to aldehyde 99 in three steps. Bis(2,2,2)trifluoroethyl)[(methoxycabonyl)methyl]-phosphonate [23] was employed for the selective formation of the cA-a, 3-unsaturated ester 100. From this Z-unsaturated ester 100, the three consecutive asymmetric units were constructed via epoxide 101 (m-CPBA), which was selectively opened by lithium dimethylcuprate to produce 102. After deprotection-protection, the alcohol 102 was converted to the phosphonium iodide 103 via a tosylate intermediate(Scheme 21). 

The final steps of the synthesis are summarized in Scheme 34. After a sequence of protection-reduction-oxydation, 171 was transformed to aldehyde 172 which was directly submitted to a Horner-Wadsworth-Emmons homologation with the requisite stabilized reagent K under Ando conditions [115] to give the corresponding a,(3-unsaturated ester 173 (Z/E > 95/5) in 84% yield. Treatment of ester 173 with 1% HC1, EtOH led to (-)-pironetin after purification (89% yield). 

Cordova and coworkers showed that prolinol silyl ethers can also operate as iminium catalysts. The Michael addition of 1-fluorobis-(phenylsulfonyl)methane to a,p-unsaturated aldehydes proceeded with high enantioselectivity (Scheme 8.6). The primary Michael adducts were transformed to aldehydes, carbo>g7lic acids, or the sulfonyl groups could... 

Nef oxidation was successfully carried out in a continuous flow system. Nitro-alkanes were effectively transformed to aldehydes or carboxylic adds using KMn04 as an oxidant, where the ultrasound pulses were applied to the flow system to avoid blocking by generated Mn02 [68]. The reaction of ethyl 4-nitrobutanoate (7.37 g) gave 5.05 g of the corresponding aldehyde in (87% yield) (Scheme 5.50). 

When boiled with Mn02, Pb02, or H2O2, a-hydroxy acids undergo oxidative cleavage, with the formation of carbon dioxide, while the acids are transformed to aldehydes or ketones with one carbon atom less in the molecule than they had originally. The reaction is carried out in the device depicted in Fig. 31. Carbon dioxide and the aldehyde or ketone are detected in the condenser test tube. 

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