Additions 2- trimethylsilyloxy-1,3-butadiene

Steric control of the Diels-Alder reaction of the enone 56 has been reported (82H2053). The ene adduct 57 (4.5%) was obtained in a reaction with 1,3-bis(trimethylsilyloxy)butadiene at 180°C, together with the main product 58 (39.5%) resulting from an ene addition. Under the same conditions, the analogous indolizidine derivative 59 gave only ene adducts. 

The octosyl acids are isolated from Streptomyces cacaoi they are part of a broader group of polyoxin antifungal nucleosides [349]. Danishefsky and co-workers [350] have reported a total synthesis of octosyl acid A featuring the hetero-Diels-Alder addition of ( )-l-methoxy-3-(trimethylsilyloxy)butadiene to a protected D-ribose-derived aldehyde. 

A review (37 refs.) on the application of molecular orbital calculations to the stereoselectivity of addition reactions of nitro-enitol derivatives has been published in Japanese. Cycloaddition of 1-acetoxy- or 1-trimethylsilyloxy-butadiene to l,2-dideoxy-l-nitro-D-g/ co-hept-l-enitol tetraacetate gave mainly the cyclohexane derivatives 41. Additions of alcohols, carbon radicals and phosphoiyl... 

Clennan, E.L. and L Esperance, R.P., The addition of singlet oxygen to alkoxy and trimethylsilyloxy butadienes. The synthesis of novel new peroxides. Tetrahedron Lett., 24,4291, 1983. 

There have been few mechanistic studies of Lewis acid-catalyzed cycloaddition reactions with carbonyl compounds. Danishefsky et ah, for example, concluded that the reaction of benzaldehyde 1 with trans-l-methoxy-3-(trimethylsilyloxy)-l,3-di-methyl-1,3-butadiene (Danishefsky s diene) 2 in the presence of BF3 as the catalyst proceeds via a stepwise mechanism, whereas a concerted reaction occurs when ZnCl2 or lanthanides are used as catalysts (Scheme 4.3) [7]. The evidence of a change in the diastereochemistry of the reaction is that trans-3 is the major cycloaddition product in the Bp3-catalyzed reaction, whereas cis-3 is the major product in, for example, the ZnCl2-catalyzed reaction - the latter resulting from exo addition (Scheme 4.3). 

A. 2-Trimethylsilyloxy-l,3-butadiene (1). An oven-dried 500-ml., three-necked, round-bottomed flask is fitted with two oven-dried addition funnels, a glass stopper, and magnetic stirrer, and placed in a 80-90° oil bath. Under an inert atmosphere, methyl vinyl ketone (25.0 g., 0.357 mole) in 25 ml. of dimethylformamide and chlorotrimethylsilane (43.4 g., 0.400 mole) in 25 ml. of dimethylformamide are added over 30 minutes to a magnetically stirred solution of triethylamine (40.5 g., 0.400 mole) in 200 ml. of dimethylformamide (Note 1). The reaction gradually darkens from colorless to yellow or dark brown, and supports a white precipitate of triethylamine hydrochloride. The reaction is set up to run overnight, or ca. 14 hours. 

Further extension of the reaction pool of Schilf bases 138 was achieved by their reaction with tran -l-methoxy-3-(trimethylsilyloxy)-1,3-butadiene (Danishefsky s diene) to give 2-substituted 5,6-didehydro-piperidin-4-ones 164 [135,136] (Scheme 10.54). The reaction is considered to be a sequence of an initial Mannich reaction between the imine and the silyl enol ether, followed by an intramolecular Michael addition and subsequent elimination of methanol. If the reaction was terminated by dilute ammonium chloride solution, then the Mannich bases 163 could be isolated and further transformed to the dehydropiperidinones 164 by treatment with dilute hydrochloric acid. This result proved that the reaction pathway is not a concerted hetero Diels-Alder type process between the electron-rich diene and the activated imine. The use of hydrogen chloride as a terminating agent resulted in exclusive isolation of the piperidine derivatives 164 formed with... 

Among the more reactive and synthetically useful dienes are doubly and triply activated alkoxy- and amino-substituted dienes, such as ( )-l-methoxy-3-(trimethylsilyloxy)-1,3-butadiene (Danishefsky s diene),( )-l-(dimethylamino)-3-(fert-butyldimethylsilyloxy)-1,3-butadiene (Rawal s diene)-, and 1,3-dimethoxy-l-(trimethylsilyloxy)-1,3-butadiene (Brassard s diene). As illustrated below, the cyclo-addition products arising from these dienes can either be hydrolyzed or treated with fluoride ion to remove the silyl group, which is followed by (3-elimination to provide conjugated cyclohexenones. 

Addition of (/ )-menthyl glyoxylate (la) to 1-trimethylsilyloxy-l,3-butadiene (2e) proceeds with a selectivity comparable to that of 1-alkoxybutadicnes. Even (f )-8-phenylmenthyl glyoxylate (1 b), bearing a very efficient chiral auxiliary, adds to 1-trimethylsilyloxy-l,3-butadiene (2e) with low diastereoselectivity17. 

Aldehydes obtained by oxidation of the C-6 position of carbohydrates are highly diastereose-lective dienophiles. Addition of diene 10b to the galactose derived aldehyde 9 in the presence of boron trifluoride - diethyl ether complex leads to a single adduct 11, while the addition to the ribose derived aldehyde 12 produces adduct 13 with a d.r. [(25,35 )/(21 ,31 )] 94 69. Eu(fod)3 catalyzed addition of 12 to ( )-l-methoxy-3-trimethylsilyloxy-l,3-butadiene (14) produces adduct 1543. 

In a synthesis of the tricychc skeleton of FR901483 (45), Bonjoch and Sole reported a TMG (3) promoted conjugate addition reaction of nitroalkane to methyl acrylate. Reaction of methyl acrylate (40) and nitro acetal 41 [9,10], obtained from Diels-Alder reaction between nitroethylene and 2-(trimethylsilyloxy)-l,3-butadiene, gave nitro ester 42 in 71% yield. The ester 42 was further converted to the spiro compound 43, and a palladium promoted cyclization reaction led to the azatricyclic skeleton 44 (Scheme 7.7). 

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