Allylsilanes allyltrimethylsilane

Coupling with Allylsilanes. Allyltrimethylsilanes react with the bromooxazinone in the presence of Zinc Chloride in THF... 

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... 

Si. rra(pentafluorophenyl)boron was found to be an efficient, air-stable, and water-tolerant Lewis-acid catalyst for the allylation reaction of allylsilanes with aldehydes.167 Sc(OTf)3-catalyzed allylations of hydrates of a-keto aldehydes, glyoxylates and activated aromatic aldehydes with allyltrimethylsilane in H2O-CH3CN were examined. a-Keto and a-ester homoallylic alcohols and aromatic homoallylic alcohols were obtained in good to excellent yields.168 Allylation reactions of carbonyl compounds such as aldehydes and reactive ketones using allyltrimethoxysilane in aqueous media proceeded smoothly in the presence of 5 mol% of a CdF2-terpyridine complex (Eq. 8.71).169... 

As expected, there was no formation of stilbenes or a dinitrile product and, more surprisingly, in all of the reactions reported only 5-7% of the allyltrimeth-ylsilane self-metathesis product was observed. It was proposed that this lack of allylsilane self-metathesis was due to the steric bulk of the TMS group reducing the reactivity of the Me3SiCH2 substituted alkylidene. In a more recent report by Blechert and co-workers it was noted that allyltrimethylsilane and its hydrocarbon equivalent (4,4-dimethylpent-l-ene) had comparable reactivities in the cross-metathesis reaction [28], further suggesting that the selectivity arises from steric rather than electronic effects. 

Only recently a selective crossed metathesis between terminal alkenes and terminal alkynes has been described using the same catalyst.6 Allyltrimethylsilane proved to be a suitable alkene component for this reaction. Therefore, the concept of immobilizing terminal olefins onto polymer-supported allylsilane was extended to the binding of terminal alkynes. A series of structurally diverse terminal alkynes was reacted with 1 in the presence of catalytic amounts of Ru.7 The resulting polymer-bound dienes 3 are subject to protodesilylation (1.5% TFA) via a conjugate mechanism resulting in the formation of products of type 6 (Table 13.3). Mixtures of E- and Z-isomers (E/Z = 8 1 -1 1) are formed. The identity of the dominating E-isomer was established by NOE analysis. 

Allylsilanes in the presence of fluoride ion can be used in place of the Grignard reagents, the reaction of allyltrimethylsilane and bis(tributyltin) oxide giving allyltributyltin in 96% yield.68... 

The addition of an allyl metal to a-amino aldehydes has been used by Vara Prasad and Rich (Scheme 12)J23l After the addition step, the allyl group is oxidized to a carboxylic acid and lactonized. Then, the a-carbon of the lactone is alkylated stereoselectively. These investigators also systematically examined the addition reaction to determine its diastereo-selectivity. The highest diastereoselectivity was obtained when allyltrimethylsilane was used in the presence of tin(IV) chloride. An increase in the steric bulk of the protecting group and of the side chain also resulted in a better diastereoselection. Alternatively, Taddei and co-workers 24-26 used a 2-(halomethyl)allylsilane and the side chains were introduced by nucleophilic substitution of the halogen (Scheme 13). 

E)-Allylsilanes These silanes can be prepared regio- and stereoselectively by hydroalumination of (chloromethyl)dimethylsilyl-l-alkynes (1) to give the cis-adduct 2. Reaction of CH3Li (3 equiv.) with 2 results in (E)-allyltrimethylsilanes (3). 

Allyl phosphates, 506 Allylsilanes, 43, 71-72, 529, 575 Allyl sulfones, 512 Allyltitaniiun ate complexes, 376-377 Allyltri-n-butyltin, 15-16 Allyltrimethylsilane, 16-20, 532 Allyltrimethyltin, 20-21 Almusone, 51 Alpine Boranc, 429 Alumina, 22-24 Aluminum amalgam, 24-25 Aluminum ate complexes, 17 Aluminum chloride, 25-28, 100 Aluminum chloride-ethanethiol, 28-29 Aluminum isopropoxide, 29, 296 Amidoalkylation, 16-17 Amidomercuration, 317 Animation, 221 Amino acid esters, 360... 

Z)-Allyltrimethylsilanes.1 Reaction of aldehydes with 2-trimethylsilylethy-lidinetriphenylphosphorane has been used to convert aldehydes into allyltrime-thylsilanes as a mixture of (E)- and (Z)-isomers (9,492). Replacement of triphen-ylphosphine by tris(2-methylphenyl)phosphine enhances (Z)-selectivity, particularly in reactions with aliphatic saturated aldehydes. These aldehydes can be converted into the (Z)-allylsilanes (Z/E > 94%) with 1, and with use of BuLi at 0° for generation of the phosphorane. 

Several methods promoted by a stoichiometric amount of chiral Lewis acid 38 [51] or chiral Lewis bases 39 [52, 53] and 40 [53] have been developed for enantioselective indium-mediated allylation of aldehydes and ketones by the Loh group. A combination of a chiral trimethylsilyl ether derived from norpseu-doephedrine and allyltrimethylsilane is also convenient for synthesis of enan-tiopure homoallylic alcohols from ketones [54,55]. Asymmetric carbonyl addition by chirally modified allylic metal reagents, to which chiral auxiliaries are covalently bonded, is also an efficient method to obtain enantiomerically enriched homoallylic alcohols and various excellent chiral allylating agents have been developed for example, (lS,2S)-pseudoephedrine- and (lF,2F)-cyclohex-ane-1,2-diamine-derived allylsilanes [56], polymer-supported chiral allylboron reagents [57], and a bisoxazoline-modified chiral allylzinc reagent [58]. An al-lyl transfer reaction from a chiral crotyl donor opened a way to highly enantioselective and a-selective crotylation of aldehydes [59-62]. Enzymatic routes to enantioselective allylation of carbonyl compounds have still not appeared. 

The reaction of (S)-phenylglycinol-derived oxazolidines 215 with allyltrimethylsilane and propynyltrimethylsilane lithium reagents, afforded 3-aminoalcohols with a vinylsilane or alkynylsilane appendage 216 and 217. The same reaction, performed in the presence of Ti(OiPr)4 gave allylsilane and allenylsilane derivatives 218 and 219 <02JOC1496>. 

Generally, the Lewis acid-promoted allylation of aldehydes with allyltrimethylsilanes proceeds via carbonyl activation. However, the SnCU-promoted allylation with allylsilanes bearing a coordinate site is rationalized by a transmetallation mechanism, in which allyltrichlorostannanes work as the actual allylating agents (Equation... 

The allyltrimethylsilane -+ allylamine transformation is characterized by high regioselecti-vity. With arylamines, both cis- and trans-allylsilanes form trans-allylamines. With sterically undemanding alkylamines 3-aminoalk-l-enes are formed with sterically demanding alkyl-amines mixtures of 3-aminoalk-1-enes and l-aminoalk-2-enes, and with bulky alkylamines only 1-aminoalk-2-enes are formed1. 

Titanium(lV) is a powerful but selective Lewis acid which can promote the coupling of allylsilanes with carbonyl compounds and derivatives. In the presence of titanium tetrachloride, benzalacetone reacts with allyltrimethylsilane by 1,4-addition to give 4-PHENYL-6-HEPTEN-2-ONE. Similarly, the enol silyl ether of cyclopentanone is coupled with f-pentyl chloride using titanium tetrachloride to give 2-(tert-PENTYL)CYCLOPENTANONE, an example of a-tert-alkylation of ketones. 

Methylenecyclopentanes. 2-Acetoxymethyl-3-allyltrimethylsilane (1) adds to a variety of electron-deficient alkenes in the presence of catalytic amounts of tetrakis(triphenylphosphine)palladium(0) and l,2-bis(diphenylphosphino)ethane to afford methylenecyclopentanes. The allylsilane 1 is prepared in four steps from methallyl alcohol. 

Silver(I) compounds are often used as promoters for substitution reactions of aliphatic halides with carbon nucleophiles. A cyclic (8-bromo ether 29 can be reacted with allyltrimethylsilane (30) imder the influence of AgBp4, yielding a mixture of ally-lated products 31 and 32 (Sch. 7) [15]. Product 31 is formed by direct substitution of the bromine atom in ether 29 by an allyl group and isomeric ether 32 arises from the carboxonium ion which is generated by debromination and subsequent [l,2]-hydrogen shift. A synthesis of optically active 4-allylazetidinone 33 (Ft = phthalimido) has also been achieved by employing the silver-promoted substitution reaction of 4-chloro-azetidinone 34 with allylsilane 30 [16]... 

Allylsilanes work as allylating reagents if the transient )8-silyl cation smoothly collapses with desilylation to form a carbon-carbon double bond. In certain circumstances, however, desilylation is retarded and becomes a slower process than a second path, which might be an unusual yet synthetically interesting reaction. Reaction of allyltrimethylsilane with a,/3-unsaturated carbonyl compounds in the presence of... 

Similar reactions, but not accompanied by the silyl migration, have also been reported. When a bulky allylsilane is reacted with benzoylformates, the product obtained is an oxetane, as shown in Eq. (100) [270]. If this reaction is executed with allyltrimethylsilane, the expected homoallyl alcohol is produced in good yield. When, moreover, interception of the /3-silyl cation with a neighboring nucleophile is faster than desilylation, even the trimethylsilyl group is preserved in the product (Eq. 101) [271]. 

Usefiil levels of stereoselectivity were obtained in intermolecular addition reactions of C(3)-sub-stituted allylsilanes to chiral aldehydes. Lewis acids that are citable of chelating to heteroatoms have been used to direct the stereochemical course of allylsilane additions to a-alkoxy and a,p-dialkoxy carbonyl compounds. The allylation of a-benzyloxy iddehyde (94) in the presence of TiG4 and SnOt furnished products with high levels of syn stereoselection (syn-9. In contrast, under nonchelation-controlled reaction conditions (BF3-OEt2) allyltrimethylsilane reacted to form predonunantly the anti-1,2-diol product (anti-95), as shown in Scheme 45. 

For the introduction of TMS groups under acidic conditions, trimethylsilyltriflate, hexamethyldisila-zane and also allyltrimethylsilane (45) - have been successfully applied. The allylsilane offers the advantage of being stable to hydrolysis. The mechanism proposed for its reaction with alcohols is shown in equation (12). It involves an initial protonation of the double bond. The 1-silylisopropyl cation formed is then attacked by the alcohol at the silicon to produce the silyl ether and propene. 

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