Mukaiyama-type reactions

However, the analogous reactions of 1-Me with various enol silyl ethers 23 in the presence of titanium tetrachloride at - 78 °C, led directly to the products 21 a - c [26 a, 33] of Mukaiyama-type reactions [34] in moderate yields (Scheme 6). 

A Mukaiyama-type reaction of trimethylsilyloxyfuran with the nitrone of lactaldehyde leads to hydroxylated piperidines following reduction of the isoxazolidine intermediates (Scheme 122) <19970PP485>. 

Direct methods mentioned above are generally only practicable with tertiary aldehydes. In the case of secondary and primary aldehydes ee values achieved are still too low. Nevertheless, direct methods are important supplementary alternatives to the Mukaiyama-type reactions. 

Mukaiyama-type reaction of cobalt-alkyne complexes with ketene acetals gives the syn product exclusively, a reaction used as a key in a relay to bengamide E (Scheme 201). Total synthesis of blastomycinone utilizing a Mukaiyama-type reaction has been reported (Scheme 202). It is interesting to note the complete reversal of selectivity compared to the uncomplexed aldehyde (Scheme 203). 

Although both aldehydes and ketones also participate in the directed aldol reaction, the former are generally more reactive, as is exemplified in Eq. (6) [45]. Thus, the aldol reaction of an enol silyl ether with an aldehyde could be performed in the presence of a ketone. Equation (6) also demonstrates that the base (LDA)-mediated aldol reaction and the Mukaiyama-type reaction took place at the different position in a complementary manner to give the isomeric aldols. 

In this review we will attempt to highlight the most important contributions toward the realization of a catalytic, enantioselective, vinylogous Mannich reaction and show the current state of the art. This chapter is organized in such a way that vinylogous Mannich reactions of preformed silyl dienolates in Mukaiyama type reactions will be discussed first followed by direct vinylogous Mannich reactions of unmodified substrates. 

The catalytic, enantioselective, vinylogous Mannich reaction has recently emerged as a very powerful tool in organic synthesis for the assembly of highly functionalized and optically enriched 6 amino carbonyl compounds. Two distinctly different strategies have been developed. The first approach calls for the reaction of preformed silyl dienolates as latent metal dienolates that react in a chiral Lewis acid or Bronsted acid catalyzed Mukaiyama type reaction with imines. Alternatively, unmodified CH acidic substrates such as a,a dicyanoalkenes or 7 butenolides were used in vinylo gous Mannich reactions that upon deprotonation with a basic residue in the catalytic system generate chiral dienolates in situ. 

In previous investigations we could show that carbohydrate enones with the electrophilic terminus of the unsaturated carbonyl system at the anomeric carbon react with silyl enol ethers under catalysis of titanium tetrachloride, i. e. in a Mukaiyama-type reaction, to give the corresponding C-glycosides in high diastereoselectivity. The high stereocontrol observed could be explained in terms of a strongly adjusted cycloaddition-like transition state. This... 

Preformed enolates such as silyl enol ethers can he used as donors in the addition of a, 8-unsaturated aldehydes (Mukaiyama-type reaction). In this reaction the DNBA salt is preferred usually as stronger acids result in decomposition of the silyl ether. Both acyclic ejco-enolates and 2-silyloxy furan derivatives were seen to undergo 1,4 addition with enals in the presence of a catalytic amount of 1 (20 mol %). This latter transformation allows easy entry to enantiomerically enriched butenolides, and has been applied to the s)uithesis of spiculisporic acid (eq 8). 

Carbonyl Activation Reactions Including Mukaiyama-Type Reactions 10.5.1... 

In 1993, Bolm introduced chiral copper complex 49 and applied it in the first metal-catalyzed asymmetric Baeyer-Villiger reaction. Under Mukaiyama-type reaction con-... 

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