Acyclic silyl dienolates

In 2008 our group reported the first example of a catalytic, enantioselective, vinylogous Mannich reaction of acyclic silyl dienolate 30 with imines (Table 5.5) [14]. 

Phosphoric acids 32 and 35 have been successfully employed as chiral Bronsted acid catalysts for vinylogous Mannich reactions of acyclic silyl dienolates with imines (Table 5.5 and Scheme 5.10). Why does the exchange of a para methyl group for a tert butyl group on the 3,3 aryl groups within the BINOL backbone have such a pronounced effect on the enantioselectivity of the reaction although this position appears to be quite remote from the reaction center ... 

A tunable and highly regio- and diastereo-selective addition of acyclic silyl dienolates (6) to several a-fluoroalkyl sulfinylimines (7) has been developed. By appropriate 0 choice of the Lewis acid catalyst, two new chiral a-fluoroalkyl amines (8) and (9) have been obtained in good yields and excellent diastereoselectivities (up to >99 1 dr), respectively (Scheme 3). The high regio- and diastereo-selectivities of different Lewis acid-catalysed reactions have been explained by different transition states. In the case of the TMSOTf-catalysed reaction, the -configuration of the newly formed chiral carbon centre in products (9) could be explained by a non-chelated transition state in which... 

An asymmetric version of the vinylogous Mannich reaction has also been implemented in the total synthesis of various alkaloids. For example, Schneider and coworkers combined A-p-methoxyphenylnicotinimine 230 and the acyclic silyl dienolate 229 in the presence of 3mol% of a chiral... 

The first systematic investigation toward Lewis acid catalyzed vinylogous Mukaiya ma Mannich reactions was reported by the group of Ojima in 1987 who showed that acyclic vinylketene silyl 0,0 acetals 10 reacted with imines activated by stoichio metric amounts of TiCU to furnish either 5 amino 2 alkenoates 11 or 5,6 dihydro pyridones 12 selectively in excellent yields depending upon the substitution of the silyl dienolate employed (Scheme 5.4) [5]. Although 2 methyl substituted vinylketene acetal 10a gave rise to acyclic 5 amino 2 alkenoates 11 exclusively, 3 methyl substi tuted vinylketene acetal 10b furnished 5,6 dihydropyridones 12 as the sole products. 

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