Aldehydes thiolesters

The method outlined here competes well with the method developed earlier by Danheiser, et al.618 Its superiority is based on the fact that phenyl ester enolates give almost the same results as the S-phenyl thiolester enolates. However, handling the malodorous benzenethiol for the preparation of the active acid derivative and during workup of the p-lactone can be avoided. In addition, phenol is much cheaper than benzenethiol. The method is well suited for the preparation of p-lactones from symmetrical and unsymmetrical ketones. In addition to 3,3-dimethyM-oxaspiro[3.5]nonan-2-one, ( )-3-ethyl-1-oxaspiro[3.5]nonan-2-one and (3R, 4R )- and (3R, 4S )-4-isopropyl-4-methyl-3-octyl-2-oxetanone were prepared by this procedure in high yields (Notes 11 and 12). In the case of unsymmetrical ketones the less sterically crowded diasteroisomer is formed preferentially. With aldehydes as the carbonyl component the yields are unsatisfactory, because of the competitive formation of 1,3-dioxan-4-ones.6... 

Photolysis of phenyl 2-thenoate leads to a 3 2 mixture of ortho and para Fries rearrangement products (Scheme 109) (74H(2)423). The photolytic rearrangement of a thiolester to a thiopyrone has been investigated with thiophenecarbothioic acid S-aryl esters as substrates (79LA2043). In the case of the 2-carbothioic acid esters, a 3-bromo substituent is necessary for this rearrangement. On the other hand, such a substituent is not necessary for the 3-carbothioic acid derivatives. In both cases, aldehydes may also be formed, sometimes as the main products (Scheme 110). 

A palladium-catalysed reduction of ethyl thiolesters to aldehydes with triethylsilane has been proposed by Fukuyama [2611. The reaction, coupled with a mild conversion of carboxylic acids to thiolesters (see [261], footnote 2), affords a versatile method for the overall transformation of... 

RCOOH - RCHO.1 This reaction can be conducted in two steps conversion of RCOOH to the ethyl thiolester, which is reduced by triethylsilane catalyzed by Pd/C to an aldehyde (equation I). This method is suitable for conversion of optically active amino acids to amino aldehydes without racemization. 

Enantioselective synthesis ofa-hydroxy acid derivatives. Recently, Aggarwal has reported an enantioselective approach to the synthesis of a-hydroxy acid derivatives using trans- 1,3-dithiane- 1,3-dioxide. For example, reaction of trans-1,3-dithiane-1,3-dioxide with an aromatic aldehyde liberates the alcohol which is protected as the tetrahydropyranyl (THP) ether the resulting product may then be subjected to a Pummerer reaction, using trifluoroacetic anhydride, to give a thiolester. Transthiolesterification of this product using LiSEt gives the... 

Oxidation of aldehydes Sodium chlorite proved far more selective than MnOa or AgO-NaCN (2,369) for oxidation of the a,/3 -unsaturated aldehyde 1 to the acid 2 without attack on the secondary hydroxyl group. The lactonization of 2 also presented a problem because of the presence of the enone group. The pyridyl thiolester method (6,246-247) was not successful. Lactonization with triphenylphosphine and diethyl azodicarboxylate (7, 405-406) gave the desired lactone in about 1% yield. However, the yield was improved to 8% when 2 was treated with the preformed betaine 3 from P(C6Hs)3 and C2H500CN=NC00C2H5. 

Oxidizing an aldehyde to an acid, creating a mixed acid anhydride in the process . The thiolester can be phosphorylized to give 1,3-bis PGA ... 

Before reference] In the preparation of an aldehyde from a thiolester (I) by desulfurization with Raney nickel, 1,2-dianilinoethane is added to trap the aldehyde as the 1,3-diphenyltetrahydroimidazole derivative (2) and so prevent its reduction. 

The geometry of enolborinates of thiolesters depends mainly upon the nature of the sulfur substituent. Masamune and coworkers [691] have shown that the reaction of thiophenyl propionate (MeCI COSPh) with 2.14 (R = OTf) leads to E-6.85, while triethylmethylthiol propionate (MeCH2COSCEt3) leads to Z-6.85 (Figure 6.75). A similar trend is observed in the reaction of MeCI COS-tert-Bu with 6.83 (X = Br) [1248], The reaction of Z-enolborinates Z-6.85 generated from 2.14 (R = OTf), 2.61 (R = OTf) or 6.83 (X = Br) with aldehydes is highly diaste-... 

The reactions of aldehydes with enoxysilanes of ketones usually exhibit poor stereoselectivity. Enoxysilanes derived from esters and thiolesters, on the other hand, give good results. Chirality has been introduced either on the Lews acid or by using an ester of an enantiopure alcohol. As in the case of enolate reactions, one or two new stereocenters may be created. All these reactions take place at low temperatures, and they are sometimes limited by the instability of certain ketene silylacetals. 

Setzt man die leicht darstellbaren Thiosaure-S-athylester 214 iso) mit aktivem Raney-Nickel in Gegenwart von YUden 117 um, so reagiert der aus dem Thiolester und Raney-Nickel bei 0 °C intermediar entstehende Aldehyd 352 mit 117 zum ungesattigten Ester 353 der zum Teil... 

Thiolesters, which are electronically more similar to ketones than esters because of the weak overlapping of the C(2p) and S(3p) orbitals, can undergo a wide variety of further synthetic transformations and are therefore very attractive reagents. The staggered transition structures for the Lewis acid mediat reaction of E and Z thiolester silyl ketene acetals with an aldehyde are summarized in Figure 1. It is assumed that the Lewis... 

By treating E or Z thiolester trimethylsilyl ketene acetals with SnCl4 the corresponding a-trichlorostannylthiolester 7 was obtained in good yield. 7 reacts with various aldehydes with a selectivity complementary to that observed with the silyl ketene acetals. ... 

Additions of stereogenic enolsilanes to aldehyde 8 are reported in Table III. Excellent ratios were obtained with thiolester silyl ketene acetals and TiCl4 as a result of chelation control (C-3,C-4 anti) and syn simple stereoselection (C-2.C-3 syn). 

The explanation for this excellent selectivity is the following both the (lS,2R)-N-methylephedrine derived silyl ketene acetal 19 and (S) 44 have an intrinsic preference for establishing a 2R.3S absolute configuration at C-2,C-3, as is evident fix>m the reaction of 19 with the achiral aldehyde 24 (see above) and tom the reaction of (S) 44 with the achiral thiolester derived silyl ketene acetals (see Table HI, entries 1,2,7,8). 

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