Silylated acetylene derivative

Simple cyclobutanes do not readily undergo such reactions, but cyclobutenes do. Ben-zocyclobutene derivatives tend to open to give extremely reactive dienes, namely ortho-c]uin(xlimethanes (examples of syntheses see on p. 280, 281, and 297). Benzocyclobutenes and related compounds are obtained by high-temperature elimination reactions of bicyclic benzene derivatives such as 3-isochromanone (C.W. Spangler, 1973, 1976, 1977), or more conveniently in the laboratory, by Diels-Alder reactions (R.P. Thummel, 1974) or by cycliza-tions of silylated acetylenes with 1,5-hexadiynes in the presence of (cyclopentadienyl)dicarbo-nylcobalt (W.G, Aalbersberg, 1975 R.P. Thummel, 1980). 

Owing to their stability and low nucleophilicity, metal acetylides are less reactive toward Cjq than other lithium organyls or Grignard reagents [11]. Though the reaction is slower and higher reaction temperatures are necessary, various acetylene derivatives of Cjq could be obtained. The first acetylene Cjq hybrids were (trimethyl-silyl)ethynyl- and phenylethynyl-dihydro[60]fullerene, synthesized simultaneously... 

In a different pattern, by using silylated acetylenes, substituted pyridazines are obtainable217 from the tetrazine derivative 401 in a diene-type reaction, first introduced by Carboni and Lindsey218. Via this reaction 4-TMS- (402) and 4,5-bis(TMS)-3,6-bis(methoxycarbonyl)pyridazine (403) can be achieved in very high yield, being inert against acid catalyzed desilylation (Scheme 59). 

A variety of alkynyl derivatives, including trimethylsilyl acetylene and terminal acetylene derivatives, have also been prepared by delithi-ation reactions with N3P3F6 (77, 79). The terminal silyl group of the trimethylsilyl acetylene derivatives has been substituted by H using KF and EtOH. The alkynyl groups of some of these substituted phos-phazenes have been found to react with Co2(CO)8, forming Co2(CO)6 complexes (77). 

Silyl-substituted acetylenes. The hyperconjugative interaction between the C=C moiety and SiH3 as well as CH3 groups of local C3v symmetry has been discussed extensively as one of the best examples of how to parametrize LCBO-MO models by PE spectroscopic M e state energies (Section IV.E). The ionization patterns of the following mono- and disilyl acetylene derivatives are also reported in the literature153 (cf. Table 62). 

A common approach is the reaction of halogenoalkylsilanes with alkali metal (lithium, sodium)110,111 or magnesium (Grignard)112 derivatives of acetylene to form silylated acetylenes which can be illustrated by the synthesis of TMS-acetylenes (182/57a) (equation 84). The reaction can be slightly modified by using bis(TMS)-sulfate (184) as silylating agent (equation 85)113. 

The classical route to bisilylacetylenes is the reaction of the di-Grignard derivative of acetylene (188) (equation 88)116. Also, the reaction of tetrachloroethene (53) with lithium and Me3SiCl in THF at — 78 °C gives rise to 189 (equation 89)114. Alternatively, the application of methyllithium to halogenated alkanes or alkenes with subsequent employment of bromo- or fluorosilanes affords bis-silylated acetylenes (equation 90)115. 

Lewis-acid-promoted alkylations of silylenol ethers and silyl ketene acetals [195] with Co-complexed acetylenic acetals [196] and acetylenic aldehydes [197,198] (Scheme 4-56) also proceed with fair to excellent syn diastereoselectivity, in contrast to the low selectivity reactions of the free acetylenic derivatives [199, 200]. Reactions of the complexed aldehydes with lithium enolates are stereospecific, with (Z)-enolates giving syn selectivity and ( )-enolates anti selectivity [201]. The complementary stereoselectivity of the crossed aldol reactions of free and cobalt-complexed propynals with silyl ketene 0,S-acetals has been elaborated by Hanoaka exclusive syn selectivity is exhibited by the complexes and high anti selectivity is found with pro-... 

Acetylenic ethers and esters represent an important class of functionalized acetylene derivatives of the hypothetical alkynols, RC=COH. The chemistry of acetylenic ethers has been well developed since their first preparation about 100 years ago Several exhaustive reviews covering the literature on acetylenic ethers and their analogs up to 1985 have been published in the last 30 years. In contrast to acetylenic ethers, esters of alkynols were unknown until the mid-1980s when the first preparation of alkynyl tosylates was reported. In the following years a wide variety of alkynyl carboxylate, phosphate and sulfonate esters has been prepared from alkynyl iodonium salts. The chemistry of these novel derivatives of alkynols has been summarized in a recent review. In the last 10 years considerable interest and research activity has arisen toward alkynols themselves and such derivatives as alkynolate salts and silyl ynol ethers. The present chapter will cover the chemistry of acetylenic ethers and esters as well as related derivatives of ynols with emphasis on new developments in this subject during the last 5-10 years. 

A soln. of BU4NF in THF (1 M, containing up to 5% water) added to a soln. of 2-dimethyl(phenyl)silyl-l-phenyl-1-tributylstannylethylene in THF, and stirred at 25° for 2 h - a-tributylstannylstyrene. Y 76%. The corresponding trimethylsilyl compd. required 120 h for desilylation. This is part of a regiospecific synthesis of enestannanes from terminal acetylene derivs. F.e.s. K. Ritter, Synthesis 1989, 218-21. 

MeOH and Si react directly on a fluid bed to give (MeO)3SiH and (MeO>4Si, M(CO)2(dmpe)2Cl on reductive silylation gives the bissiloxy alkyne derivative which acidifies to the first dihydroxyacetylene complex, and silyl acetylenes prepared regioselective. The relative stability of ketene and silaketene radical cations are compared and ketene thermally eliminated from ethyl silyl acetates. ... 

C-C double bond cleavage of an enyne derivative using a metallocene derivative was reported by Takahashi and coworkers [34]. When an alkyne was treated with Cp2ZrEt2 and vinyl bromide or vinyl ether in this order after hydrolysis a 2,3-disubstituted diene derivative was obtained (Eqs. 22 and 23). Bis-silyl acetylene, aryl-substituted acetylene or cyclohexyl-substituted alkyne could be used as internal alkynes. 

This catalyst was successfully applied to the Diels-Alder reaction of propargyl aldehydes as dienophUes [12] (Scheme 1.21, Table 1.8). Though 2-hutyn-l-al and 2-oc-tyn-l-al are unreactive dienophUes, silyl- and stannyl-suhstituted a,/ -acetylenic aldehydes react with cydopentadiene readily in the presence of 20 mol% of the catalyst at low temperature to give hicyclo[2.2.1]heptadiene derivatives in high optical purity these derivatives are synthetically useful chiral building blocks. 

The regiochemistry of the hydrozirconation of disubstituted stannyl- [24, 167-170] and silyl- [171] acetylenes and boron- [118, 172-175] and zinc- [34, 126] alkynyl derivatives result in the formation of 1,1-dimetallo compounds. Hydrozirconation of alkynyliodonium salts affords alkenylchlorozirconocenes with the Zr-C bond geminal to the iodonium moiety [176]. These zirconocene complexes allowed the preparation of ( )-trisubstituted olefins (Scheme 8-20). 

The structural comparison (Fig. 3) with both the twofold tris(trimethylsilyl)methyl substituted acetylene and 1,4-benzene derivatives (Fig. 1) as well as with the literature data [6a] for hexa-kis(rm.butyl)disilane [6b] containing a SiSi bond elongated to 270 pm ( ), for the linear ( ) hexa-kis(rm.butyl)disiloxane [6c] or for di(tris(trimethylsilyl)silyl)zinc [6d] is based advantageously on a model in which the two substituent half-shells are separated along their central C3 axes by spacers of different lengths. 

A unique bis-silylation system, in which a bis(silyl)palladium intermediate is generated via recombination of two Si-Si bonds, has been developed.8,97 A bis(disilanyl)dithiane reacts with alkynes in the presence of a palladium/ isocyanide catalyst, giving five-membered ring bis-silylation products in high yield with elimination of hexamethyl-disilane (Scheme 14). The recombination, that is, bond metathesis, is so efficient that no product derived from direct insertion of acetylene into the Si-Si bonds of the bis(silyl)dithiane is formed at all. 

It is also possible to carry out a substrate-controlled reaction with aldehydes in an asymmetric way by starting with an acetylene bearing an optically active ester group, as shown in Eq. 9.8 [22]. The titanium—acetylene complexes derived from silyl propiolates having a camphor-derived auxiliary react with aldehydes with excellent diastereoselectivity. The reaction thus offers a convenient entry to optically active Baylis—Hillman-type allyl alcohols bearing a substituent (3 to the acrylate group, which have hitherto proved difficult to prepare by the Baylis—Hillman reaction itself. 

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