Allyltrimethylsilanes

The starting allyltrimethylsilane can be prepared in satisfactory yield by the procedure of Sommer. It can also be purchased from PCR Inc., Aldrich Chemical Company, Inc., Fluka A. G., Petrarch Systems Inc., and Tokyo Kasei Kogyo Co., Ltd. The checkers employed material from Petrarch. 

The use of more than 1.2 equiv of allyltrimethylsilane is essential for shortening the reaction time as well as to avoid contamination of the product by unreacted benzalacetone. 

Treatment of 2-methoxy-l-tert-butoxycarbonylpiperidine (127) with allyltrimethylsilane and TiCU gave a mixture of 2-allyl-l-rerr-butoxycarbo-nylpiperidine (128) and 3-[(trimethylsilyl)methyl]perhydropyrido[l,2-c][l,3] oxazin-l-one (129) (97JCS(P1)2163). 

The reactions of a-methyl-branched acylsilanes with 2-propenylmagnesium bromide exhibit surprisingly high diastereoselectivilies, although further improvement is accomplished by application of allyltrimethylsilane/ titanium(IV) chloride (> 100 I)27. The fluoride-induced desilylation proceeds with retention of configuration. 

The direct allylation of 2-phenylpropanal proceeds with much lower selectivity [2-propenylmagnesium bromide 73 27 allyltrimethylsilane/titanium(IV) chloride 67 33]27. 

A mixture of TMSOTf (0.1 mmol, lmol%), allyltrimethylsilane (11.5 mmol) and dichioromethane (1 ml) was cooled to -78 °C, and to this was added benzaldehyde dimethylacetal (10.5 mmol) in dichioromethane (4ml). The resulting mixture was stirred for 6h at —78°C, and then poured into saturated sodium hydrogen carbonate solution (10 ml) and extracted with ether (3 x 20 ml). The combined organic extracts were washed with brine, dried and concentrated. Chromatography on silica gel (1 20 ether hexane) gave 4-pheny]-4-methoxybut-l-ene (9.2mmol, 88%). 

TiCLi-induced conjugate addition of allyltrimethylsilane to 4-phenylbut-3-en-2-one ... 

Recently, Co(III)-allyl complexes have been described to be sulfonylated regiospecifi-cally by sulfonyl halides under irradiation232 (equation 42). Similarly, allyl methyl sulfone has been obtained from allyltrimethylsilane under copper(I) catalysis213. 

An allylsilane-generating CM using catalyst C between the sensitive /J-lactone 319 and allyltrimethylsilane served to introduce the allylsilane moiety in intermediate 320 as an inconsequential mixture (ca. 3 1) of (EIZ)-isomers in 80% yield. Cyclization of /J-lactone 320 with TiCl4 smoothly delivered cyclopentane 321 with inversion at the /J-carbon. Acid 321 was converted to key aldehyde 322 in three steps. The convergent fragment coupling was performed by a uniquely... 

In the case of alkylation using allylsilancs in the presence of aluminum chloride as a catalyst, allylsilanes containing one or more chlorine substituents on the silicon react with aromatic compounds at room temperature or below 0 C to give alkylated products. 2-aryl-1 -silylpropanes.- while allyltrimethylsilane did not give the alkylated product but instead dimerized to give the allylsilylation product.. S-itrimethylsilyli-d-itrimethylsilylrnethyl)- 1-pentene (Eq. (1 )). In the alkylation reaction, the reactivity of allylsilanes increased as the number of chlorine... 

Initial attempts to effect addition of allyltrimethylsilane with compound 132 under conditions developed in Kishi s C-glycoside work were plagued by epimerization of the acetal center subsequent to the coupling event, providing 133 as a 1 1 mixture of diastereomers (Eq. 21). Boons reported that acetal... 

The alkoxysiladioxanes described by Davis were shown to undergo selective axial addition of allyltrimethylsilane [49]. Moderate selectivity (7-13 1) was observed when the reactions were promoted by Lewis acids (TMSOTf, SnCl4), while higher selectivity was realized when a Bronsted superacid was used (Eq.23). 

The oxime 299 is silylated in the presence of catalytic amounts of TMSOTf 20 to 300, which affords, via the Beckmann fragmentation intermediate 301 and alkylation with allyltrimethylsilane 82, 66% of the seco nitrile 302 [101, 102] (Scheme 4.39). Tris(trimethylsilyl) ketenimine 303 reacts with aldehydes such as benzaldehyde in the presence of Bp3-OEt2, via the aldol adduct 304, to give the unsaturated nitriles 305, in 99% yield, and HMDSO 7 [103]. 

Of special preparative interest is 2,3-bis(trimethylsilyloxy)trimethylsilylpropane 408, readily obtained from allyltrimethylsilane 82 by hydroxylation and subsequent O-silylation, as a new means of protecting carbonyl groups. The silylated glycol... 

In the presence of catalytic amounts of TMSOTf 20 methyl pyruvate reacts with N,N-bis(trimethylsilyl)formamide 22c in CCI4 to give the silylated 0,N-acetal 433 in 83% yield ]44] this, with allyltrimethylsilane 82 and excess TMSOTf 20, after 30 h at 78 °C in CH2CI2, affords 72% of the methyl ester of 2-allyl-N-formylala-... 

Phenylpropanal 583 reacts with phenylthiotrimethylsilane 584 in the presence of TiCl4, via the 0,S-acetal 585, to give the S,S-acetal 586 [144]. Conducting the reaction in the presence of allyltrimethylsilane 82 and SnCl furnishes the allylic sulfides 587 and 588 in 3 1 ratio and 56% yield [144] (Scheme 5.45). 

Dimethyl acetals of aldehydes and ketones, for example benzaldehyde dimethyl acetal 121, and hemiacetals, react with allyltrimethylsilane 82 at -78 °C in CH2CI2, in the presence of TMSOTf 20 [169], trimethyhodosilane TIS 17 [159, 170],... 

Additions of silylated ketene acetals to lactones such as valerolactone in the presence of triphenylmethyl perchlorate in combination with either allyltrimethylsilane 82, trimethylsilyl cyanide 18, or triethylsilane 84b, to afford substituted cyclic ethers in high yields have already been discussed in Section 4.8. Aldehydes or ketones such as cyclohexanone condense in a modified Sakurai-cyclization with the silylated homoallylic alcohol 640 in the presence of TMSOTf 20, via 641, to give unsaturated cyclic spiro ethers 642 and HMDSO 7, whereas the 0,0-diethyllactone acetal 643 gives, with 640, the spiroacetal 644 and ethoxytrimethylsilane 13b [176-181]... 

Benzaldehyde dimethyl acetal 121 reacts, for example, with the silylated allylic alcohol 645, in the presence of SnCl2-MeCOCl, via an intermediate analogous to 641, to the 3-methylenetetrahydrofuran 646 and methoxytrimethylsilane 13 a [182], whereas benzaldehyde dimethyl acetal 121 reacts with the silylated homoallylalco-hol 640 in the presence of TMSOTf 20 to afford exclusively the ds 4-vinyltetrahy-drofuran 647 and 13 a [183]. A related cyclization of an a-acetoxy urethane 648 containing an allyltrimethylsilane moiety gives the 3-vinylpyrrohdine 649 in 88% yield and trimethylsilyl acetate 142 [184, 185]. Likewise, methyl 2-formylamido-2-trimethylsilyloxypropionate reacts with allyltrimethylsilane 82 or other allyltri-methylsilanes to give methyl 2-formamido-2-aUyl-propionate and some d -unsatu-rated amino acid esters and HMDSO 7 [186] (Scheme 5.56). 

Treatment of ninhydrin 431 with excess allyltrimethylsilane 82 and triflic acid in acetonitrile affords dehydrated ninhydrin 660 in 55% yield and the O-silylated product 661 in 18% yield [43] (Scheme 5.59). 

The weaker Lewis add TMSOTf 20 as catalyst gives, after 2 h at 0°C in CH2CI2, a 20 80 mixture of 805 and 806 in only 23% yield (Scheme 6.8). But this yield will probably increase either on longer reaction time at 0°C or on shorter reaction time at 25 °C On replacing one of the methyl groups in 804 by an acetylene substituent the resulting enyne adds allyltrimethylsilane 82 or anisole in the presence of TMSOTf 20 to give allenes [18]. Substituted allyltrimethylsilanes such as 808 react with the allylic silylether 807 after 70 h at 25 °C in 62% yield to a 41 59 mixture of 809 and 810 as well as 7 [17]. Closely related additions of 82 to allylic ethers or O-acetates are discussed in Refs. 17a-c. 

C-C Bond-formation from Haloalkanes with Allyltrimethylsilane... 

Because allyltrimethylsilane 82 or benzyltrimethylsilane 83 can be regarded as combinations of the hard trimethylsilyl cation and the soff allyl or benzyl anions, pyridine N-oxide 860 reacts with excess 82 or 83 in the presence of catalytic amounts of tetrabutylammonium fluoride di- or trihydrate in THF to give 2-allyl-or 2-benzylpyridines 948 and 950 [60]. The general reaction of silicon reagents such as 82 and 83 or of trimethylsilyl cyanide 18 with fluoride to generate allyl or... 

Reaction of pyridine N-oxide 860 with excess allyltrimethylsilane 82 affords, via 947, 2-propenylpyridine 948 in 53% yield as the only reaction product which can be isolated. Ehmination of trimethylsilanol 4 from 947 is apparently followed by fluoride-catalyzed isomerization of 2-allylpyridine into 2-propenylpyridine 948. 3-Methylpyridine-N-oxide 867 a is converted into 2-propenyl-3-methylpyridine in 69% yield. Likewise, fluoride-catalyzed addition of excess benzyltrimethylsilane 83 to 860 furnishes, via 949, 2-benzylpyridine 950 in 70% yield. The generated leaving group trimethylsilanol 4 reacts with excess allyltrimethylsilane 82 or benzyltrimethylsilane 83 in the presence of fluoride to give hexamethyldisiloxane (HMDSO) 7 and propylene or toluene, respectively [60] (Scheme 7.16). 

Although these reactions are formulated as ionic reactions via 947 and 949, because of the apparent partial formation of polymers and inhibition of the fluoride-catalyzed reaction of pyridine N-oxide 860 with aUyl 82 or benzyltrimethylsilane 83 by sulfur or galvinoxyl yet not by Tempo, a radical mechanism caimot be excluded [61, 62]. The closely related additions of allyltrimethylsilane 82 (cf. Section 7.3) to nitrones 976 are catalyzed by TMSOTf 20 to give, via 977, either o-unsatu-rated hydroxylamines 978 or isoxazoHdines 979 (cf also the additions of 965 to 962a and 969 in schemes 7.20 and 7.21). 

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