Aldehydes, 2-hydroxy oxidative cleavage

Cleavage of the addition product 5 can be easily performed by treatment with dilute ( 1 %) aqueous alcoholic hydrochloric acid which liberates the chiral amino alcohol 3 and an a-hydroxy aldehyde. The latter can be further oxidized to the oc-hydroxy carboxylic acid 6 with sodium chlorite33. 

Oxidative cleavage of the terminal double bond of 49 by ozonolysis to the aldehyde followed by permanganate oxidation to the acid and esterification with diazomethane produced the methyl ester 50. Dieckmann cyclisation of 50, following the procedure developed in Holton s laboratory (LDA, THF, -78 °C, 0.5 h, then HOAc, THF), gave the enol ester 5J in 93% yield (90% conversion). Decarbomethoxylation of 5J. was carried out by temporarily protection of the secondary alcohol (p-TsOH, 2-methoxypropene, 100%), and heating the resulting compound 52 with PhSK in DMF, at 86 °C (3 h) to provide 53a or, after an acidic workup, the hydroxy ketone 53b. 92% yield. 

N-Methylated y-amino-p-hydroxy acids are accessible by the usual synthetic sequences, i.e. aldol condensation or y-amino-P-oxo ester reduction, starting from the corresponding N-methylated a-amino acids, but are obtained with low diastereoselectivity. 61-63 Alternatively, Brown allylboration of the ALBoc-ALMe amino aldehyde 16 (R1 = Bzl, X=Boc, Y = Me) gives the allyhc N-methylated intermediate 27 in 64% yield and 90% de (Scheme 12). 64 Oxidative cleavage of the alkenol is performed using the two-step ozonolysis and sodium chlorite oxidation sequence. 

The reagent is effective for oxidative cleavage of a-glycols to aldehydes, of a-hydroxy ketones to an aldehyde and a carboxylic acid, and of a-diketones and a-keto iicids to acids.3... 

Novel nor-seco baccatin 99 was synthesized in 92% yield through oxidative cleavage of the A ring of 14-OH-DAB (75) with periodic acid via the hydroxy ketone intermediate 100 (Scheme 19). Protection of the 7-hydroxyl of 99 as TES ether followed by reduction of the aldehyde with sodium borohydride yielded nor-seco baccatin alcohol 101 in 80% yield. Nor-seco 13-amino-baccatins 102 and 103 were synthesized from 101 and 99a via the Mitsunobu reaction and reductive amination, respectively, in high yields (Scheme 20). 

Chiral secondary a-hydroxy aldehydes, Rf HOHCHO. The chiral acyl derivatives 3, obtained from 1 by lithiation and reaction with an aldehyde followed by Swem oxidation, can be reduced stereoselectively before cleavage to the secondary a-hydroxy aldehydes. 

The Lewis acid-promoted reaction of aldehydes with a-substituted allylsilanes affords 3-silyltetrahydrofurans, in good to high yields, with homoallyl alcohols [476-479]. The use of homochiral a-substituted allyl- and crotyldimethylphenylsilanes realizes highly diastereo- and enantioselective syntheses of tri- and tetrasubsti-tuted THF derivatives, which can be converted into 3-hydroxy-THF derivatives by oxidative cleavage of the carbon-silicon bond (Scheme 10.171) [476-478]. 

Under different reaction conditions, vicinal diol production [70] or C=C double bond oxidative cleavage to carboxylic acids occurs [59, 71], Dialdehydes are produced from cycloolefins, by tungstic acid as catalyst in t-butanol [72], Secondary alcohols yield ketones, while primary alcohols produce aldehydes or carboxylic acids [59, 68-69, 73-74], Different products are obtained from glycols, under different reaction conditions, 1,2-Diols are cleaved to ketocarboxylic acids and dicarboxylic acids [58, 75], or oxidised to a-hydroxy ketones [76], The latter can be obtained directly from the olefins, with lower selectivity [77], Lactones are formed by 1,4-diols and other a,o)-diols [78], Internal alkynes predominantly yield a,p-epoxyketones [79], or 1,2-diketones and carboxylic acids if HgfAcO) is added as the cocatalyst [80], Terminal alkynes yield a-ketoaldehydes and carboxylic acids. 

---