1- Trimethylsilyll-3-dienes

Electrochemical oxidation of l-(trimethylsilyl)dienes in MeOH affords 129 in moderate to satisfactory yield. It is worth noting that the reaction shows some diastereoselectivity (equation 109)1". 

In the synthesis of analogs of the antibiotic spectinomycin, Danishefsky and coworkers used the hetero Diels-Alder reaction to construct a precursor to install the stereochemistry on the tricyclic ring system. " Trimethylsilyl diene (145) reacts with acetaldehyde and a catalytic amount of Eu(fod)3 to give a 5.7 1... 

Danishefsky and Harvey have reported the synthesis of an important subunit in the construction of tirandamycin (Scheme 51). Trimethylsilyl diene (14) reacts with 4,5-dimethylfuran-2-carbaldehyde (184) followed by a brief treatment with TFA to give exclusively the syn pyrone (185). Pyrone (185) is reduced using LAH and subjected to a Ferrier-like rearrangement using benzyl alcohol in the presence of... 

The reaction of l,4-bis(trimethylsilyl)-l,3-butadiyne (174) with disilanes, followed by treatment with methylmagnesium bromide, produces i,l,4,4-tetra(-trimethylsilyl)-l,2,3-butatriene (175) as a major product[96]. The reaction of octaethyltetrasilylane (176) with DMAD proceeds by ring insertion to give the six-membered ring compounds 177 and 178[97], The l-sila-4-stannacyclohexa-2,5-diene 181 was obtained by a two-step reaction of two alkynes with the disilanylstannane 179 via the l-sila-2-stannacyclobutane 180[98],... 

The Boekelheide reaction has found utility in other synthetic methodology. An approach to 2,3-pyridynes made use of this chemistry in the preparation of the key intermediate 30. Treatment of 28 with acetic anhydride produced the desired pyridone 29. Lithiation was followed by trapping with trimethylsilyl chloride and exposure to triflic anhydride gave the pyridyne precursor 30. Fluoride initiated the cascade of reactions that resulted in the formation of 2,3-pyridyne 31 that could be trapped with appropriate dienes in Diels-Alder reactions. 

Organomagnesium derivatives have not so far been isolated [80JA994 80JOM(193)C13]. Bis[bis(trimethylsilyl)phosphonamide] with diphenylbutadi-yne and calcium or strontium in THE yields the TiyP)-coordinated species 129. Reaction of (THE)4Ba[P(SiMc3)2]2 with diphenylbutadiyne gives an ri -coordinated species 130 (98JA6722). 1-Chloro-and l-cyclopentadienyl-3,4-dimethyl-2,5-bis-(trimethylsilyl)-l-phosphacyclopenta-2,4-dienes both react with calcium to give... 

Methyl-7-(trimethylsilyl)oxepin and 4-methyl-4//-l,2,4-triazole-3,5-dione as dienophile undergo a Diels-Alder reaction in which the 4,6-diene structure of the seven-membered ring react. Contrary to the aforementioned reactions, the primary adduct 12 is stable and does not rearrange to a carbonyl compound.222... 

Conjugate addition, 34-5, 51-2,53, 132, 133 Conjugate hydroxymethylation, 59-60 Copper(n) bromide, 54 Copper([) chloride, 120 Copper(n) chloride, 120 Copper(i) cyanide, 7,52, 53 Copper(i) iodide, 54 Corey s internal quench, 104 Cyanohydrin trimethylsilyl ether, 137 Cycloaddition. 34,112 Cydobutane-l,2-dione, 135 Cyclohept-2-dione, 135 Cyclohex-2-enone, 52,123 Cyclohcxa-1,3-diene, 26 Cyclohexane carboxaldehyde, 22-3,69 73,78... 

In fl-trimethylsilylcarboxylic acids the non-Kolbe electrolysis is favored as the carbocation is stabilized by the p-effect of the silyl group. Attack of methanol at the silyl group subsequently leads in a regioselective elimination to the double bond (Eq. 29) [307, 308]. This reaction has been used for the construction of 1,4-cyclohexa-dienes. At first Diels-Alder adducts are prepared from dienes and P-trimethylsilyl-acrylic acid as acetylene-equivalent, this is then followed by decarboxylation-desilyl-ation (Eq. 30) [308]. Some examples are summarized in Table 11, Nos. 12-13. 

With the successful chemistry of the cymantrenes and the (cyclobuta-diene)tricarbonyl iron, the quest for tetraethynylated cyclobutadienes based on CpCo-stabilized complexes arose. Why would they be interesting Whereas all derivatives of 63 and 68 exhibit reasonable stability when their alkynyl substituents are protected by either an alkyl or a trimethylsilyl group, the desilylated parents are isolated only with difficulty and are much more sensitive. 

N-silylated imines 509 react with the Li salts of tosylmethylisonitriles to give 4,5-disubstituted imidazoles in moderate yields [93]. Acetylation of N-trimethylsilyl imines 509 with acetyl chloride and triethylamine affords 72-80% of the aza-dienes 510 these undergo readily Diels-Alder reactions, e.g. with maleic anhydride at 24 °C to give 511 [94] or with dimethyl acetylenedicarboxylate to give dimethyl pyridine-3,4-dicarboxylates [94] (Scheme 5.29). 

In the presence of catalytic amounts of Bp3.0Et2 aromatic aldehydes such as benzaldehyde are converted by bis(trimethylsilyl)selenide 604 into hexamethyldi-siloxane 7 and the corresponding trimers, for example 611 in up to 90% yield. On heating with 1,3-dienes such as 2,3-dimethylbutadiene trimers such as 611 react to give the Diels-Alder product 612 [155] (Scheme 5.49). 

The diacetal 629, prepared from the carbonyl compound and O-silylated allylic alcohols in the presence of TMSOTf 20, reacts with ( )-l-trimethylsilyl-2,4-penta-diene 630, in the presence of TMSOTf 20 in CH2CI2 at -78°C, to afford 60% 631 this undergoes Diels-Alder-cyclization at 170 °C in toluene to give a substituted... 

Danishefsky s diene).46 The two donor substituents provide strong regiochemical control. The D-A adducts are trimethylsilyl enol ethers that can be readily hydrolyzed to ketones. The (3-methoxy group is often eliminated during hydrolysis, resulting in formation of cyclohexenones. 

Methyl 2-chloro-2-cyclopropylideneacetate (4) was readily prepared in two steps from ethylene and tetrachlorocyclopropene [7], and reacted with 4-methylcyclohexa-l,3-dien-2-ol trimethylsilyl ether (62a) at 60 °C to give a complex mixture containing about equal amounts of both regioisomeric adducts 63a, 64a besides the tricyclic ketoester 65a after acidic workup (Schemes 12 and 13) [15]. Each regioisomer was a mixture of endo and exo-diastereomers. The trimethylcyclohexadiene 62b yielded, after 2 days at 100 °C and acidic work-up, the tricyclic ketoester 65b as the main product (Schemes 12 and 13) [15]. 

Regert et al. studied [9] a series of 30 Neolithic hafting adhesives from lake dwellings at Chalain (France) using an analytical procedure based on GC/MS analysis involving solvent extraction (dichloromethane) and trimethylsilylation. In the majority of the samples a series of triterpenoid compounds with a lupane structure was clearly identified on the basis of their TMS mass spectra. In particular, the presence of betulin, betulone, lupenone, lupeol and lupa-2,20(29)-dien-28-ol allowed birch bark tar to be identified. In other samples the co-occurrence of other plant biomarkers such as a-amyrin,(3-amyrin... 

Bromoalkynes also couple with vinylstannanes readily to result in enynes. Synthesis of protected enynals via cross-coupling of vinylstannanes with 1-bromoalkynes in the presence of a catalytic amount of Pd(II) has been reported (equation 143)252. Hiyama and coworkers extended the Stille methodology for sequential three-component coupling of trimethylstannyl(trimethylsilyl)acetylene with a vinyl iodide in the first step and cross-coupling of the intermediate trimethylsilylethyne with another alkenyl iodide in the presence of tris(diethylamino)sulphonium trimethyldifluorosilicate in the second step to generate a dienyne (equation 144)253. Both steps occur under palladium catalysis, in one-pot, to result in stereodefined l,5-dien-3-ynes. 

A useful application of the silver-mediated additions is 1,3 -diene synthesis by three-carbon elongation of aldehydes [48,51,53]. The bimetallic reagent 3-trimethylsilyl-l-propenylzirco-nocene chloride (A Scheme 8.23) reacts with aldehydes under the influence of a catalytic amount of Ag+ to give the intermediate zirconocene-alkoxide B, which then undergoes a Peterson-type 1,4-elimination of TMS alkoxide to stereoselectively afford ( )-dienes (fc/Z > 96 4) (Scheme 8.23). A Wittig reaction yields the same products without stereoselectivity (ca. 1 1 mixtures of E- and Z-isomers). 

The diastereoselectivity of the anodic oxidation of 1-silyl-1,3-dienes is interesting [32]. The anodic oxidation of 5-phenyl-1-trimethylsilyl-1,3-hexa-diene in methanol gives a mixture of two diastereomers in 4 1 ratio. On the basis... 

The (trimethylsilyl)ethynyl group of the products can undergo further transformation to furnish substituted dienes or even alkynes. 

Diels-Alder reactions. In the presence of trimethylsilyl triflate, this orthoester is converted into a 1,1-diethoxyallyl cation, CH2=CHC+(OC2H5)2, which reacts with 1,3-dienes at -78° — 0° to give the corresponding adducts of ethyl acrylate. In the presence of trimethylsilyl triflate, ethyl acrylate can undergo Diels-Alder reactions, but higher temperatures are required and yields are lower. 

Butynone 93 and tetrasubstituted allene 94 combine to form acetyl cyclopenta-diene 95 (Eq. 13.30) [32]. The annulation does not proceed in satisfactory yield in the case of unsubstituted trimethylsilyl allene 96 (Eq. 13.31) [32]. This is presumably due to diminished stabilization of the cationic intermediates in the case of 96, which allows competing reaction pathways to erode the yield. 

An outstandingly reactive diene is l-methoxy-3-(trimethylsilyloxy)-l,3-butadiene ( Danishefsky s diene ) 4, prepared by the action of trimethylsilyl chloride on the ketone 3 in the presence of zinc chloride/triethylamine (equation 7)6. The reaction of diethyl mesoxalate with Danishefsky s diene gives the dihydropyran 5 with the (trimethylsily-loxy)dienes 6 and 7, mixtures of dihydropyrans are obtained, in which the meta-isomers predominate (equations 8 and 9)7. 

In a similar study, Park has shown125 that cyclic dienes other than cyclo-pentadiene will also undergo a [4 + 2] cycloaddition reaction with the (trimethylsilyl)alkynylcarbene complex (184.b). When 184.b was reacted with 1,3-cyclohexadiene in THF, the diene complex 191 was isolated along with the vinylketene complex 192, which was prone to hydrolysis during column chromatography as expected.123 When 192 was stirred with silica gel and water in hexane, an almost quantitative conversion to the aldehyde complex 193 was observed. 

The unusual amino acid (S)-2-amino-(Z)-3,5-hexadienoic acid (269), which is a component of the toxic y-glutamyl dipeptide isolated from the defensive glands of the Colorado beetle [209], has been synthesized along Scheme 17, after two initial attempts had proved unsuccessful due to the instability of 269 towards various oxidation conditions [210]. Scheme 17 relies on the hydrolysis of an ortho ester to generate the required carboxylic acid. Thus, the L-serine aldehyde equivalent 270 was treated with ( )-l-trimethylsilyl-l-propene-3-boronate to give the addition product 271. Reaction of 271 with KH gave the stereochemically pure (Z)-diene 272. Mild acid treatment of 272 followed by... 

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