Formylation selectivities

The hydroindole 548 was also converted to ( )-haemanthidine (382) and ( )-tazettine (397) (215). The transformation of 548 to 549 was achieved by sequential N- and O-formylation, selective hydrolysis of the formate ester, and then 0-acetylation. The elaboration of 549 to 551 was then effected via Bischler-... 

Stigmasterol from soy bean extracts can be selectively ozonolyzed on the side-chain double bond. The 20-formyl group formed is converted to the enamine with piperidine. This can be oxidized to progesterone. 

The alkyl derivatives of thiazoles can be catalytically oxidized in the vapor phase at 250 to 400°C to afford the corresponding formyl derivatives (21). Molybdenum oxide, V2O5, and tin vanadate are used as catalysts either alone or with a support. The resulting carbonyl compounds can be selectively oxidized to the acids. 

Production of Acrolein Dimer. Acting as both the diene and dienoplule, acrolein undergoes a Diels-Alder reaction with itself to produce acrolein dimer, 3,4-dihydro-2-formyl-2id-pyran, CgHg02 [100-73-2], At room temperature the rate of dimerization is very slow. However, at elevated temperatures and pressures the dimer may be produced in single-pass yields of 33% with selectivities greater than 95%. 

Formylation of folate (3) or hydrolysis of 5,10 — CH+ — folate (9) gives (6R,3)-5-formyltetrahydrofohc acid (6) (5-HCO-H folate) (55). On the other hand, (63)-5-HCO-H4 folate is obtained by selective crystaUi2ation in the form of its calcium salt from the diastereomeric mixture of (63, R)-5-HC0-H4 folate (56). 10-Formyltetrahydrofohc acid (7) is a coen2yme in purine synthesis which is synthesi2ed by hydrolysis of 5,10 — CH+ — folate (9) or by hydrogenation of lO-CHO-folate (57). 

The yield of the more active RRR-a-tocopherol can be improved by selective methylation of the other tocopherol isomers or by hydrogenation of a-tocotrienol (25,26). Methylation can be accompHshed by several processes, such as simultaneous halo alkylation and reduction with an aldehyde and a hydrogen haUde in the presence of staimous chloride (27), amino alkylation with ammonia or amines and an aldehyde such as paraformaldehyde followed by catalytic reduction (28), or via formylation with formaldehyde followed by catalytic reduction (29). 

Selective formylation of the 3,20-diketone (1) with ethyl formate gives the 2-hydroxymethylene ketone (2). Subsequent methylation and acidic de-formylation affords the 2a-monomethyl product (4) in 50% yield. 

Because aldehydes react with aminofluorosulfuranes more readily than ketones, keto aldehydes can be selectively fluorinated at the formyl group [94, 183] Haloacetaldehydes react with DAST to give bis(l-fluorohaloethyl) ethers as the only or main products [170] (equation 96)... 

It is thus apparent that the selectivity of a reagent toward thiophene and benzene can differ appreciably, and this difference in selectivity is also strongly noticeable in the proportions of 2- and 3-isomers formed. Although in certain reactions no 3-isomer has been detected, appreciable amounts have been found in other reactions. Thus 0.3% of the 3-isomer has been found in the chlorination of thiophene.- Earlier results indicated that 5-10% 3-nitrothiophene is formed in the nitration of thiophene and a recent gas-chromatographic analysis by Ostman shows that the mononitrothiophene fraction contains as much as 16% of the 3-isomer. It appears that gas-chromatographic analysis should be very useful for the detection of small amounts of 3-isomers in other substitution reactions. However, from routine analyses of IR spectra, it appears to the present author that the amount of 3-isomers formed in acylation, formylation, and bromina-tion of thiophene are certainly less than a few per cent. 

A variety of 1,3-oxazolidines have been used as chiral formyl anion equivalents for addition to aldehydes. Thus, for example, reaction of N-protected norephedrine with Bu3Sn-CH(OEt)2 gives 48, and transmetallation with BuLi followed by addition of benzaldehyde affords the expected adduct 49. The selectivity at the newly formed alcohol center is poor, but the situation can be salvaged by oxidation and re-reduction, which affords the product 50 with >95% d.e. It is then a simple matter to hydrolyze off the oxazolidine, although the resulting hydroxyaldehydes... 

The applicability of the Reimer-Tiemann reaction is limited to the formylation of phenols and certain reactive heterocycles like pyrroles and indoles. Yields are usually below 50%. In contrast to other formylation procedures, the Reimer-Tiemann reaction is ort/zo-selective it is therefore related to the Kolb e-Schmitt reaction. 

Electrochemically generated nickel is very selective for the reduction of ai compounds into anilines, in which alkenyl, alkyhyl, halo, cytino, formyl, ind benzyloxy groups are not affected. Sodium snlfide has been used for the selective reduction of at group in the presence of aliphatic nitro groups (Tq. 6.44. ... 

It is noteworthy that a clear enhancement of selectivity for the linear hydro-formylation product is observed only with cdpp (Table 5.2-1, entry e). With all other ligands, the n/iso ratios are in the 2 to 4 range. While this is in accordance with known results in the case of PPI13 (entry a) and dppe (entry c) (in comparison to monophasic hydroformylation [69]) and also with reported results in the case of Natppts (entry b in comparison to the biphasic hydroformylation of 1-pentene in [BMIM][PF(3] [46]), it is more remarkable for the bidentate metallocene ligand dppf... 

In contrast to the Vilsmeier formylation the formylation with trimethyl orthoformate in trifluoroacetic acid proceeds with high selectivity so that only the /3-monoformylated deuteroporphyrin derivatives 8 are formed without any methinc substituted or diformylated products.1073 6... 

Selective electrophilic attack has also been demonstrated, for example, during nitration,48 chlorination,37-49 bromination,32 acylation and formylation.32k... 

If a chiral aldehyde, e.g., methyl (27 ,4S)-4-formyl-2-methylpentanoate (syn-1) is attacked by an achiral enolate (see Section 1.3.4.3.1.), the induced stereoselectivity is directed by the aldehyde ( inherent aldehyde selectivity ). Predictions of the stereochemical outcome are possible (at least for 1,2- and 1,3-induction) based on the Cram—Felkin Anh model or Cram s cyclic model (see Sections 1.3.4.3.1. and 1.3.4.3.2.). If, however, the enantiomerically pure aldehyde 1 is allowed to react with both enantiomers of the boron enolate l-rerr-butyldimethylsilyloxy-2-dibutylboranyloxy-1-cyclohexyl-2-butene (2), it must be expected that the diastereofacial selec-tivitics of the aldehyde and enolate will be consonant in one of the combinations ( matched pair 29), but will be dissonant in the other combination ( mismatched pair 29). This would lead to different ratios of the adducts 3a/3b and 4a/4b. 

This section deals with investigations specifically aimed at producing homopolymers and copolymers of furan carbonyl compounds by the selective opening of the carbonyl bond. The many reports on polymerization of 2-furaldehyde which in fact deal with complicated acid-catalysed resinification reactions which involve both the formyl group and the furan ring are reviewed in Chapter VI. 

The main application of the enzymatic hydrolysis of the amide bond is the en-antioselective synthesis of amino acids [4,97]. Acylases (EC 3.5.1.n) catalyze the hydrolysis of the N-acyl groups of a broad range of amino acid derivatives. They accept several acyl groups (acetyl, chloroacetyl, formyl, and carbamoyl) but they require a free a-carboxyl group. In general, acylases are selective for i-amino acids, but d-selective acylase have been reported. The kinetic resolution of amino acids by acylase-catalyzed hydrolysis is a well-established process [4]. The in situ racemization of the substrate in the presence of a racemase converts the process into a DKR. Alternatively, the remaining enantiomer of the N-acyl amino acid can be isolated and racemized via the formation of an oxazolone, as shown in Figure 6.34. 

Cieplak apphed this effect to the explanation of the shift of selectivity in the reactions of the pentamethylcyclopentadienes 21,19, and 20 having substiments of formyl, vinyl, and (hydroxyimino)methyl moiety at the 5-positions [14]. He pointed out that the observed result is consistent with the notion that in the case of formyl moiety the hyperconjugative effect is enhanced by lone pair back-donation due to ... 

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