Acylthiazolidinethiones

Acyliminium ions can be used in enantioselective additions with enolates having chiral auxiliaries, such as A-acyloxazolidi nones or A-acylthiazolidinethiones. 

Titanium enolates of various carbonyl compounds play an increasingly important role in Mannich-type reactions with different electrophiles. Recently, Liotta and co-workers reported a novel diastereoselective addition of chloro-titanium enolate 80 of iV-acylthiazolidinethione to various types of O-methyl oximes to afford the desired anti-azetines, precursors of a,/3-disubstituted /3-amino carbonyl derivatives 82 (Scheme 32).109... 

Although iV-acyloxazolidinones 88 and iV-acylthiazolidinethiones 90 lead to an anti aldol, the respective products 89 and 91 present a different anti configuration. Consequently, the corresponding derived magnesium enolates exhibit the opposite face selection in these reactions. On the basis of previous results involving enolates of various metal complexes such as boron, titanium, lithium or sodium enolates, the (Z)-metal enolate... 

The enantioselective addition (<97% ee) of /S-keto esters (127) to unsaturated A-acylthiazolidinethiones (128), catalysed by Ni(II) Tol-BINAP Lewis acid com- plexes (130), has been reported no external base was required.166... 

Addition of [1-ketoesters to unsaturated A -acylthiazolidinethiones 836 is catalyzed by the Ni(ll) Tol-BINAP Lewis acid complex 837. The initial addition products 838 cyclize upon treatment with base to afford enantiopure 3,4-dihydropyran-2-ones 839 in excellent yield (Scheme 236, Table 35) <2005JA10816>. 

Chiral acylthiazolidinethiones such as 26 can readily be prepared from commercially available amino acids in three steps12 (Scheme 2.2k). They have been employed as a synthetically useful auxiliary in diastereoselective aldol reactions.13 The magnesium-catalyzed aldol reaction of the thiazolidinethione 26.S with cin-namaldehyde afforded 27 as a major diastereomer in 87% yield. Interestingly, compound 27 is the opposite anti-aldol diastereomer to that seen with the oxa-zolidinone 23S. 

Because the acylthiazolidinethione-derived magnesium-enolate exhibits the opposite face selection to that of its oxazolidinone counterpart, it is necessary to assume that the thione C = S moiety is not coordinating to the Mg center in... 

The chlorotitanium enolates derived from AT-acyloxazolidinones 3.17, N-acyloxazolidinethiones 3.18 and iV-acylthiazolidinethiones 3.19 undergo highly selective and efficient aldol reactions with aldehydes. The iST-acyloxazolidinethione 3.18 and N-acylthiazolidinethione 3.19 auxiliaries are also easier to cleave. 

The Ni(II) Tol-BINAP-catalyzed enantioselective orthoester alkylation of N-acylthiazolidinethiones 158 is carried out using 5 mol% of (5)-Ni(ll) Tol-BINAP 157 to provide 159 in good yields and with excellent enantioselectivities <05JA10506>. 

Esters. With promotion by DMAP the methanolysis of Af-acyloxazolidinethiones and A -acylthiazolidinethiones is achieved at room temperature. 

DMAP can also be used in the removal of the thiazolidinethione moiety fromiV-acylthiazolidinethiones to the corresponding benzyl esters. DMAP was found to be superior to other bases including imidazole, 2,6-lutidine, and DBU (eq 17). 

Similarly, MgBr2-Et20 was proved to be an effective catalyst in the di-astereoselective direct anti-aldol reaction of chiral AT-acylthiazolidinethiones in the presence of triethylamine and chlorotrimethylsilane. Grood yields (56-93%) and diastereoselectivities (up to 19 1) were obtained for a variety of N-acylthiazolidinethiones and unsaturated aldehydes (140). 

Ultimately, a set of conditions which utilizes 1 equiv of tita-nium(IV) chloride, 1 equiv of (—)-sparteine, and 1 equiv of A/-methylpyrrolidinone as a ligand for the metal center was developed to avoid the need for greater than 1 equiv of (—)-sparteine (eq 12). These enolization conditions are also effective for A acyloxazolidinones and A -acylthiazolidinethiones. ... 

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