Aldehydes allyltrimethylsilane

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... 

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]. 

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]... 

Aldehydes with a- or p-benzyloxy substituents react with allyltrimethylsilane in the presence of SnCl4 to give high yields of product resulting from chelation control.97... 

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... 

Indolizidine alkaloids. The key step in a new stereocontrolled synthesis of these alkaloids, such as castanospermine (5), depends upon the diastereoselective reaction of an azagluco aldehyde with allylmetal reagents catalyzed by Lewis acids (12, 21-22). Thus reaction of allyltrimethylsilane with the aldehyde 1 and TiCL, (excess) in CH2C12 at - 85° results in the product 2, formed by selective chelation of the ot-amino aldehydo group with TiCl4. The product can be converted into 5... 

The synthesis of the smaller fragment methyl esters 144-147 was completed as depicted in Scheme 20. Chelation-controlled allylation of aldehydes 135-138 prepared by chromium(VI) oxidation of alcohols 122,123,133, and 134 with allyltrimethylsilane (139) in the presence of titanium(IV) chloride proceeded... 

Iodine is known to catalyze the condensation of aldehydes, benzyl carbamate and allyltrimethylsilane to homoallylic amines. However, in this case the involvement of an in sitn prepared [MejSi] species was suggested to be the active catalyst [235], An iodine catalyzed acetalization of carbonyl compounds was reported, where the active catalyst was believed to be hydroiodic acid [236],... 

The first procedure is a one-pot sequential process in which the acetal is formed from the aldehyde in a Bi(OTf)3-catalyzed reaction with trialkylorthoformate and the corresponding alcohol. After the aldehyde was consumed, the remaining alcohol was removed under reduced pressure. Acetonitrile, allyltrimethylsilane, and additional Bi(OTf)3 were added and the desired homoallyl ethers were obtained in moderate to good yields (Scheme 10). 

A three-component one-pot procedure was also developed. This method involves stirring the aldehyde, trialkylorthoformate, and allyltrimethylsilane in CH3CN in the presence of a catalytic amount of Bi(OTf)3. The homoallyl ethers were again obtained in moderate to good yields with a more simple and straightforward procedure (Scheme 11). 

Monocyanohydrins of P-diketones.3 In the presence of TiCl4, acetyl cyanide reacts with enol silyl ethers of ketones at - 78° to afford monocyanohydrins of diketoncs in excellent yield. The corresponding reaction with enol silyl ethers aldehydes proceeds in only about 35% yield. A low temperature is essential for this reaction. A similar reaction is possible with allyltrimethylsilane. 

Acetonylation.1 In the presence of TiCl or BF3 etherate allyltrimethylsilane undergoes conjugate addition to a,/ -enones. The 5,e-enones formed are converted by ozonation or KMnO K 10 to o-keto aldehydes. Wacker oxidation can be used to obtain methyl ketones. 

N-Monoprotected aldehydes reacted according to the non-chelation-controlled model. The best diastereocontrol (syn/anti, 20.6 1) was achieved with allyltrimethylsilane in the presence of tin tetrachloride. A similar method was used in the synthesis of the aminoglycosidic fragment of calicheamycin yj [36]. 

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). 

Homoallylic ethers Reaction of aldehydes with allyltrimethylsilane and Cl2Ti(OR)2 (prepared from LiOR and TiCl4) results in homoallylic ethers in 50-95% yield. 

Alkynylation of aldehydes.3 The reaction of alkynylmetals with chiral aldehydes shows no or slight diastereoselectivity, but in the presence of TiCl4, alkyn-yltributyltin reagents react with the steroid aldehyde 1 with about 9 1 diastereoselectivity. TiCl4-catalyzed reaction of 1 with allyltrimethylsilane or allyltributyltin also shows similar and comparable diastereoselectivity. 

Lithium-Ammonia, 158 Potassium hydride, 257 Tetrakis(triphenylphosphine)palla-dium(O), 289 Tributyltin chloride, 315 8,e-Unsaturated aldehydes and ketones Allyltrimethylsilane, 11 Lead tetraacetate, 155 Unsaturated amides Bis(benzonitrile)dichloropalladium(II), 34... 

Tetrahydropyrans bearing halides at C4 can be accessed by a modified Taddei-Ricci reaction. The reaction involves condensation of allyltrimethylsilane, aldehydes and a cyclic acetal 371 in the presence of a Lewis acid to afford all ry -tetrahydropyrans 372 as a single diastereomer. The reaction proceeds via anion mediated ring closure of oxonium ion intermediate 373 (Scheme 89). This methodology was successfully applied to the synthesis of a model compound bearing all the structural motifs present in the eastern subunit of okadaic acid <1997TL2895>. 

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. 

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... 

Allyltriorganosilanes react with activated C-N double bonds such as iminium salts and Lewis acid-coordinated imines at the y-position to give homoallylamines.14,118 For example, in the presence of BF3, iV-acylimines generated in situ by the reaction of aldehydes or acetals with carbamates are efficiently allylated with allyltrimethylsilanes (Equation (26)).119,119a,12° The use of homochiral crotylsilanes such as 20 leads to highly diastereo- and enantioselective synthesis of homoallylamines (Equation (27)). a Allenylation of the iV-acylimines can be performed with propargylsi lanes. 

Aldehydes, ketones, and acetals react with allyltrimethylsilane in the presence of a catalytic amount of BiX3 (X = C1, Br, OTf) to give homoallyl alcohols or homoallyl alkyl ethers (Equation (52)).91-93 The BiX3-catalyzed allylation of aldehydes and sequential intramolecular etherification of the resulting homoallylic silyl ethers are involved in the stereoselective synthesis of polysubstituted tetrahydropyrans (Equation (53)).94,95 Similarly, these Lewis acids catalyze the cyanation of aldehydes and ketones with cyanotrimethylsilane. When a chiral bismuth(m) catalyst is used in the cyanation, cyanohydrines are obtained in up to 72% ee (Equation (54)). a-Aminonitriles are prepared directly from aldehydes, amines, and cyanotrimethysilane by the BiCl3-catalyzed Strecker-type reaction. 

A combination of chlorodimethylsilane and allyltrimethylsilane effectively promotes the deoxygenative allylation of aromatic ketones to terminal alkenes in the presence of a catalytic amount of InCl3 (Equation (94)). The choice of solvent is important the reaction of acetophenone proceeds only in dichloromethane or 1,2-dichloroethane. Aldehydes and aliphatic ketones give complicated mixtures. 

Evidence for a closed transition-state model was gathered on the basis of the diastereoselectivity in reactions of pentacoordinate allylic silicates. Bis(l,2-benzenediolato)allylsilicates la and lb, which can be prepared via the reactions of E- and Z-crotyltrichlorosilanes with dilithium catecholate, react with aromatic aldehydes to give the corresponding homoallylic alcohols 2 in high yields3 (Scheme 3.2a). Unlike allyltrimethylsilane,4 the allylation reactions of... 

Chiral homoaXlylic alcohols. The chiral acetals 2 formed from an aldehyde and 1, undergo titanium-catalyzed coupling with allyltrimethylsilane with marked stereoselectivity. Highest stereoselectivity is usually obtained with the mixed catalyst TiCl4-Ti(0-/-Pr)4 (6 5). Cleavage of the chiral auxiliary, effected by oxidation to the ketone followed by P-elimination, provides optically active alcohols (4) with —95% ee (equation I).1... 

Regioselective Peterson reaction. Aldehydes react with the anion of an (a-al-koxy)allyltrimethylsilane (1) at both a- and y-positions. Addition of HMPT favors reaction at the y-position, whereas addition of Ti(0-/-Pr)4 (1 equiv.) results in exclusive reaction at the a-position to give an (E)-l, 3-dienol ether (2). These products are readily hydrolyzed to vinyl ketones (3).4... 

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