Silyloxy dienes

The mechanistically quite similar double Michael reaction of 2-silyloxy dienes and enones has been shown recently to go via a similar two-step mechanism rather than a Diels-Alder cycloaddition S. Kobayashi, Y. Sagawa, H. Akamatsu and T. Mukaiyama, Chem. Lett., 1988, 1777. 

Methods based on the cyclization of diene derivatives have been described. Thus, chalcose (152) has been synthesized by a cyclocondensation reaction of the silyloxy diene 166 with acetaldehyde (Scheme 50).241... 

As shown in Scheme 15, the thiophene-based silyloxy diene 90 was adopted as an homologative reagent in the opening vinylogous aldol coupling to glyceraldehyde 11. 

Casiraghi, G. Rassu, G. Zanardi, E Battistini, L. Asymmetric Access to Functional, Structurally Diverse Molecules Exploiting Five-Membered Heterocyclic Silyloxy Dienes, Adv. Asym. Synth., Vol. 3, Hassner, A., Ed., JAI Press, Stamford, CT, 1998. 

It has been reported that several transition metal complexes catalyze the hetero-Diels-Alder reaction between a variety of aldehydes, in particular benzaldehyde, and Danishefsky s diene (Sch. 52). With the [CpRu(CHIRAPHOS)] complex the ee is modest (25 %) (entry 1) [192]. The chiral complex VO(HFBC)2 performs better in this reaction (entry 2) [193]. In experiments directed towards the synthesis of anthra-cyclones, this complex was used in cycloadditions between anthraquinone aldehydes with silyloxy dienes. One example is shown in Sch. 53 [194]. Compared with the chiral aluminum catalyst developed earlier by Yamamoto and co-workers [195], the vanadium catalyst results in lower enantioselectivity but has advantages such as ease of preparation, high solubility, stability towards air and moisture, and selective binding to an aldehyde carbonyl oxygen in the presence of others Lewis-basic coordination sites on the substrate. 

D-Glyceraldehyde, the smallest of the sugars, was also used to synthesize carba-sugars. As shown in Scheme 8.13, it was first protected as the acetonide and the carbonyl group in 39 was submitted to a vinylogous cross aldohsation with a furan silyloxy diene to selectively give... 

Rassu, G, Zanardi, F, Battistini, L, Casiraghi, G, The synthetic utility of furan-, pyrrole- and thiophene-based 2-silyloxy dienes, Chem. Soc. Rev., 29, 109-118, 2000. 

V-Silylated vinylcopper reagents are acylated with acid chlorides followed by palladium-catalyzed 1,5-sigmatropic rearrangement to form silyloxy dienes in moderate yield (equation 57)." ... 

The major development in the Lewis acid catalyzed reaction came in 1981 when Danishefsky and coworkers reported that ZnCh and BF3-OEt2 catalyze the cyclocondensation of silyloxy dienes with unactivated aldehydes. The use of these Lewis acid catalysts permits a variety of simple aldehydes to be used in the reaction (Table 2). Danishefsky also critically evaluated the mechanism and stereochemistry of the cyclocondensation reaction with a series of dienes, aldehydes and catalysts. These studies resulted in conditions to control the relative and absolute stereochemistry of the reaction and allowed the use of this chemistry in natural product synthesis. 

Vinylogous aldol reaction of heterocyclic silyloxy dienes and its synthetic application 00PAC1645. 

Danishefsky used a variety of silyloxybutadienes in Diels-Alder reactionsin place of alkoxy and acetoxy derivatives. Treatment of these cycloadduct siloxy derivatives with fluoride (sec. 7.3.A.i) will unmask an enol moiety, which tautomerizes to the carbonyl under very mild conditions. Silyloxy dienes have become very popular for this type of reaction. In Weinreb s synthesis of phyllanthine,150 imine 144 reacted with diene I43151 in the presence of Yb(OTf)3 to give 145. Hydrolysis converted this functionality to the conjugated ketone 146 in 84% overall yield. The previous development of 143 as a reagent was due to several unsuccess-... 

The synthetic plan for leucascandrolide A by Paterson and co-workers in 2003 involved the incorporation of all oxygenated stereocenters in a substrate controlled manner. The synthesis began with the construction of the 2,6-cw-tetrahydropyran. An asymmetric hetero-Diels-Alder reaction of silyloxy diene 2.122 with aldehyde 2.121, catalyzed by the Jacobsen chromium Schiff base complex [116], afforded 2,6-cw-tetrahydropyranone 2.123 (80 %, dr >20 1, ee >98 %). Reduction of the... 

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