Diels 1-trimethylsilyl-1,3-butadiene

Allylic and Propargylic Alcohols. Allyl silanes (22), formed as Diels-Alder adducts from 1-trimethylsilyl butadiene, can be converted regiospecifically into allylic alcohols (Scheme 8), either with allylic rearrangement, using peracids, or without rearrangement. The latter transformation is achieved by first reacting the allyl... 

In 1995, these authors applied this methodology to the first total synthesis of the biosynthetically and unusual marine natural products, gracilins B and Thus, the key step of this synthesis was the enantioselective Diels-Alder reaction of 2-((trimethylsilyl)methyl)-butadiene with A-(2-iert-butylphenyl)maleimide in... 

Simple dienes react readily with good dienophiles in Diels-Alder reactions. Functionalized dienes are also important in organic synthesis. One example which illustrates the versatility of such reagents is l-methoxy-3-trimethylsilyloxy-1,3-butadiene (.Danishefsky s diene) 1 Its Diels-Alder adducts are trimethylsilyl enol ethers which can be readily hydrolyzed to ketones. The /j-mcthoxy group is often eliminated during hydrolysis. 

Diels-Alder reactions of bis(trimethylsilyl)acetylene.1 A catalyst obtained from TiCl4 and (C2H5)2A1C1 (1 20) effects Diels-Alder reactions of this acetylene with butadiene and methyl-substituted derivatives to form l,2-bis(trimethylsilyl)-cyclohexa- 1,4-dienes in 70-78% yield (equation I). The yield is low (15%) only when R, R4 = CH3,R2,R3 = H because of polymerization of the diene. The products undergo thermal dehydrogenation at 240° to form l,2-bis(trimethylsilyl)ben-zenes in almost quantitative yield. This cycloaddition has been effected in low yield with an iron-based catalyst. 

Chiral (.S, .S )-diazaaluminolidine catalyst brought about the first highly enantioselective catalytic Diels-Alder reaction of an achiral C2v-symmetric dienophile with an achiral diene. Addition of 2-methoxybutadiene to A-o-tolylmaleimide in the presence of 20 mol % (5,5)-diazaaluminolidine gave rise to the cycloadduct in 98% yield and 93% ee one recrystallization from i-PrOH-hexane furnished the enantiomerically pure compound [57] (Eq. 8A.34). The Diels-Alder reaction of 2-((trimethylsilyl)methyl)butadiene and A-aryimaleimide promoted by this catalyst has been successfully applied to the enantioselective total synthesis of Gracilins B and C [58],... 

Dichlorobis(diisopropoxy)titanium(IV). Titanium(IV) chloride. Zinc iodide. DIELS-ALDER REACTIONS 2-Acetoxy-I-methoxy-3-trimethylsilyloxy-1,3-butadiene. 4-Acetoxy-1 -trimethylsilyl-1,3-butadiene. Benzyl irans-l,3-butadiene-l-carbamate. 1,3-Bis(/-butyldimethylsilyloxy)-2-aza-1,3-diene. 2,3-Bis(trimethylsilyl)methyl-1.3-buladiene (10-1,3-Dimethoxybutadiene 4-I)iniethyhnnino 1,1,2... 

Conversion of —Si (013)3 to —OH. Searle chemists have used this transformation in a synthesis of 4-demethoxydaunomycinone (6). Thus aryl-trimethylsilanes were known to be converted into aryl trifluoroacetates by lead tetrakistrifluoroacetate (4, 282-283) the Searle chemists found that this trifluoroacetoxylation was also applicable to benzyltrimethylsilane. With this information and knowing that 1,3-butadienes substituted by trimethylsilyl groups show selectivity in Diels-Alder reactions, they then devised the route shown in the formulation. The first step involved a Diels-Alder reaction to give 3. This product... 

DIELS-ALDER REACTIONS 3-Acetyl-4-oxazoline-2-one. 1,3-Bis(trimethylsilyl-oxy)-l,3-butadiene. 1-Chloro-l-di-methylaminoisoprene. 1,3-Dihydroiso-thianaphthene-2,2-dioxide. 4,6-Di-methoxy-2-pyrone. Furane. trans -Methoxy-3-trimethylsilyloxy-l,3-butadiene. Trichloroethyl trans-1,3-butadiene-1-carbamate. Trichloro-1,2,4-triazine. 

The A building block 138 was reached by Clark and co-workers 107) by Diels-Alder reaction of l-ethoxy-3-[(trimethylsilyl)-oxyl]-2-methyl-1,3-butadiene with ethyl-( )-2-acetoxyacrylate. 

Hetero-Diels-Alder Reactions of Ketones. Ketonic substrates such as ethyl pyruvate (eq 9, R =Me, R = OEt) do not react with simple dienes such as cyclopentadiene or 1,3-cyclohexadiene in the presence of (5, 5)-/-Bu-box and a metal salt as catalyst. However, using activated dienes such as /ranf-l-methoxy-3-[(trimethylsilyl)oxyl]-l,3-butadiene (Danishefsky s diene), a hetero-Diels-Alder reaction with ethyl pyruvate and similar substrates catalyzed by 10 mol% of Cu[(5, 5)-/-Bu-box] (OTf)2 takes place in good yields and enantioselec-tivities (eq 9). Surprisingly, it was even possible to reduce the catalyst loading to only 0.5 mol % without affecting the yield of the product, and in some cases the enantiomeric excess was even improved. 

Independently, 2,3-bis[(trimethylsilyl)methyl)-1,3-butadiene (193) was shown to be a similar conjunctive reagent for tandem Diels-Alder reactions (Scheme 46). In this case the initial cycloadducts were subjected to an oxidative bis-desilylation with NBS and the resulting 1,2-dimethylenecyclohexanes were directly submitted to the second Diels-Alder step, as demonstrated by the reaction sequence (193) (194) -> (195). 

An elegant total synthesis of the semiprotected form of lincosamine was realized by Marshall and Beaudoin [116]. An aldehyde derived from destomic acid (6-amino-6-deoxy-L-g/yc ro-D-ga/acto-heptonic acid) was derived in a similar way from a L-serinal derivative via hetero Diels-Alder addition to 1-ethoxy-3-[(trimethylsilyl)oxy]-4-benzyloxy-1,3-butadiene [142]. A similar method was applied to the preparation of a semiprotected form of anhydrogalantinic acid, a component of the antibiotic galantin I [142]. 

Just catalytic amounts of the title reagent are required to efficiently mediate in the conversion of Diels-Alder adducts of l-methoxy-3-[(trimethylsilyl)oxy]- 1,3-butadiene (Danishefsky s diene) to cyclohexenones (eq 114). Dilute HCl or concentrated acid lead to a greater percentage of side products. 

In studies by Card, Diels-Alder reaction of carbohydrate enones with 1-[(trimethylsilyl) oxy]-1,3-butadiene, followed by treatment of the products with DDQ in refluxing benzene proved to be an efficient route to benzannelated pyranosides (9). 

A theoretical study of endo-selectivity in the Diels-Alder reaction between butadienes and cyclopropene has shown that neither electron delocalization nor the electrostatic interaction shows preference of enrto-addition over e o-addition. l-Amino-3-siloxybuta-1,3-dienes are highly reactive dienes which show high endo-selectivity in Diels-Alder additions. The aldehyde 2-methylene-5-trimethylsilyl-pent-4-yn-l-al (161) has been shown to be a versatile dienophile reacting with Danishefsky s diene (162) to produce 4 + 2-cycloadducts (163) with endo-selectivity (Scheme 62). " ... 

Siloxylated butadienes have been popular for some time as the diene component in Diels-Alder reactions and numerous applications have been reported this year. Examples of their use in the synthesis of highly functionalized aromatics are given in Scheme 23, which shows the immediate result of cyclization in each case. Included with the products obtained in this way are dermoglaucin, ° daunomycinones, a milbemycin /Sa unit, and L-Dopa. They have also played a key part in the synthesis of the saturated carbocyclic systems fomannosin (127), coriolin (128), and seychellene (129).fra s-l-Benzenesulphonyl-2-(trimethylsilyl)ethylene (130) is a useful dienophile in the Diels-Alder reaction... 

Coupling Reactions to Dienes and Enynes. The silyl bromide (1) participates readily in copper or transition metal-mediated coupling reactions to produce 1,3-butadienes, which are very useful s)mthetic intermediates. For example, 2,3-bis[(trimethylsilyl)methyl]-1,3-butadiene (8), derived from the oxidative dimerization of cuprate (2) (M = Cu) is useful for rapid construction of multicyclic systems via tandem Diels-Alder reactions, as depicted in eq 15 The diene 2-dimethylaminomethyl-3-... 

Diels-Alder Reactions. ( )-I-Trimethylsilyl-1,3-butadiene undergoes Diels-Alder reactions with the usual dienophiles, with unimpaired endo stereoselectivity, but at a somewhat slower rate than 1,3-butadiene itself (eq 1). The regioselectivity with un-symmetrical dienophiles is poor (eq 2). The adducts are allylsilanes, which react with electrophiles in the usual way (eqs 3 and 4) to give cyclohexenes with a double bond shifted from the original position. ... 

Table 1 Diels-Alder reactions of 1-trimethylsilyl-l,3-butadiene (1) OTMS OTMS OTMS...

In an alternative approach, the Diels-Alder adduct (144), obtained from the enedione (143) with l-methoxy-3 [(trimethylsilyl)oxy]-1,3-butadiene, was further transformed into the a-iodo ester (145). Exposure of the latter to iodotrimethylsilane furnished the 8-lactone (146), an attractive ABCD ring precursor to the quassinoids (106). 

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