Dethioacetalization

Deterioration, failures due to, 26 982 Deterioration technologies, 15 468470 Dethioacetalization reaction, microwaves in, 16 559-561... 

BnPh3PHS05 was used for deprotection of oximes and semicarbazones to their parent carbonyl compounds under microwave irradiation. Similarly, dethioacetalization of 1,3-dithiolanes and 1,3-dithianes by BnPhsPHSOs in aprotic solvents was also reported . In both these reactions a catalytic amount of bismuth chloride was necessary. 

When using dithioacetals as intermediates the most tedious step is often their hydrolysis to carbonyl compounds. As a consequence, many methods have been developed to realize that conversion and, in their review [43], Grobel and Seebach give experimental details for most of the procedures known at that time. In view of the fundamental importance of dethioacetalization, we now describe some promising new methods that have appeared since. 

Anodic oxidation provides also an efficient way for the regeneration of a carbonyl group from its dithioacetal derivative. This method proved to be useful in dethioacetalization of oses [51] and of acyl silanes [52]. 

Desulfonylation Lithium-Ammonia, 158 Lithium triethylborohydride, 168 Magnesium-Methanol, 170 Sodium dithionite, 281 Sodium naphthalenide, 294 Desulfurization Lithium aluminum hydride-Bis(cyclopentadienyl)nickel, 158 Lithium l-(dimethylamino)naph-thalenide, 165 Lithium-Ethylamine, 158 Dethioacetalization (see Hydrolysis of thioacetals and -ketals)... 

Keywords thioacetal, dethioacetalization, clayfen, microwave irradiation, ketone,... 

The approach has found further applications in cleavage of benzyl esters, dethioacetalization, deoximation, and desilylation reactions [34],... 

BTI is a very efficient reagent for the regeneration of aldehydes and ketones from their dithiacetals. As usual, reaction conditions are very mild, with yields impressively high. A great variety of substrates have in this way undergone dethioacetalization, so that BTI has become the reagent of choice for this transformation. The fate of the sulphur-containing moiety has not been identified. 

Some substrates incorporating an enolic ester functionality and a 1,3-dithiane ring reacted in an unexpected way, when their dethioacetalization was attempted, affording aldol-type condensation products e.g. [45] ... 

Dethioacetalization.1 The combin C6H5OPOCl2, and Nal converts acetals to 1 but has little, if any, effect on thioacetal addition of DMF converts thioketals into at room temperature in 1-17 hours in 70- ... 

Dethioacetalization.6 This reaction can be effected with QH5I(OCOCF3)2 (1) in aqueous methanol (9 1) or acetonitrile at 25° without effect on ester, nitrile, hydroxyl groups, or unsaturated bonds. 

Dethioacetalization. Ethylene dithioacetals are cleaved to carbonyl compounds by nitronlum tetrafluoroborate in excellent yield. Other somewhat less effective reagents are N0 HS04 and NaNOa or NaNOj in TFA. 

Hydrolysis of thioacetals (7, 364). TTN has been used for selective dethioacetalization of the bis thioketal 1 to the mono thioketal 2. The paper includes examples of hydrolysis of simpler thioacetals. ... 

DETHIOACETALIZATION Methyl Huoro-sulfonate. Sulfuric acid. 

Halogenations. The i halogen that can be used to metavanadate, molybdate, halogenating aromatic comp Dethioacetalization amd regenerated from the protect and cyano groups suffer oxk... 

Dethioacetalization and dethioacetalization. Aldehydes and ketones are regenerated from the protected derivatives by NaBOj-Na CO, in HOAc. Aromatic amino and cyano groups suffer oxidation by this reagent. 

Dethioacetalization. Thioacetals can be cleaved to the ketones in high yield by treatment with trimethyloxonium tetrafluoroborate (6 equivalents) followed by addition of water (cf. 4, 528-529). 

Dethioacetalization. Dithioacetals are hydrolyzed by treatment with cold, concentrated sulfuric acid (10 min.).9 This method was used in a synthesis of dihydro-jasmone (4). Thus treatment of (2) with concentrated sulfuric acid yields (3). The vinylic... 

Although the yield of (3) is rather low, dethioacetalization of simple ketones usually proceeds in high yield (90-98 %). 

Another synthesis of (-)-allosamizoline (8) was also carried out using the glucoseamine derivative 44 by an intramolecular cycloaddition of a nitrile oxide to an olefin as a key step (Scheme 5). ° lodination of 44 followed by reductive 3-elimination using zinc in THF afforded the 5-enofuranose 46, whose reaction with ethanethiol in cone. HCl followed by silylation with TBSOTf afforded 47. Dethioacetalization of 47 with HgCl2-CaC03 followed by treatment of the resulting aldehyde with NH2OH afforded the oxime 50, which underwent intramolecular cycloaddition to produce the isoxazoline 51. Alternatively, treatment... 

The completion of the total synthesis of FK506 (1) is described in Scheme 34. The coupling of the two segments 222 and 230 was accomplished by phosphine oxide-mediated HW olefination. The addition of 222 to 230 afforded a separable 1 1 mixture, and the less polar diastereomer yielded ( )-olefin 231. After selective removal of the TES group, esterification of 231 with (S)-A-Boc-pipecolic acid (232) under DCC-DMAP conditions followed by dethioacetalization afforded aldehyde 233. The Evans aldol reaction of 233 with 218d installed a glycolate unit, and hydrolysis of the chiral auxiliary followed by TES protection provided 234 ready for macrocyclization. The macrolactamization of 234 was effectively... 

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