Aldehydes intramolecular diene coupling

E.iii. Aldehydes and Ketones as TVapping Agents Intramolecular Diene Coupling... 

For use of conjugated dienes as nucleophilic partners in catalytic intramolecular reductive couplings to aldehydes, see ... 

In 2005, MacMillan reported an enantioselective organocatalytic intramolecular Diels-Alder reaction (IMDA) of a,p-unsaturated aldehyde and diene, as well as the application in the asymmetric synthesis of solanapyrone D (6), Scheme 3.1 [5]. Later, Danishefsky and Christmann individually reported the total synthesis of UCS1025A (9) by coupling reaction with MacMillan aldehyde (8) [6]. The malim-ide analogue 10 of the telomerase inhibitor UCS1025A (9) was also prepared by Christmann et al. by modified MacMillan s conditions (10 mol% catalyst loading in nitromethane, affording 74% yield and >99% ee after a sequence of recrystallization and oxidation). Scheme 3.2 [7]. 

Silastannative coupling of 1,3-diene and aldehydes is achieved both in inter- and intramolecular fashions (Equations (116) and (117)).277 Interestingly, the reaction is catalyzed by nickel(0) complexes, whereas a platinum complex is used for simple 1,4-silastannation of 1,3-diene.278... 

It is proposed that the reaction proceeds through (i) oxidative addition of a silylstannane to Ni(0) generating (silyl)(stannyl)nickel(n) complex 25, (ii) insertion of 1,3-diene into the nickel-tin bond of 25 giving 7r-allylnickel intermediate 26, (iii) inter- or intramolecular allylation of aldehydic carbonyl group forming alkoxy(silyl)nickel intermediate 27, and (iv) reductive elimination releasing the coupling product (Scheme 69). 

A number of new Ni-catalyzed protocols have been developed recently for the coupling of carbonyl compounds and unsaturated substrates such as alkynes or 1,3-dienes. For instance, a three-component intramolecular coupling (alkyne/aldehyde/hydrosUane) has led to the formation of bicyclic N-heterocycles. A number of similar inter- and intramolecular coupling reactions have been developed into useful synthetic routes (Scheme 27). 

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