With Allylstannane

The chemistry of o-benzoquinones, especially their involvement in cycloadditions, has been the subject of extensive investigations in recent years (Nair and Kumar 1994, 1996a, b). In contrast, their aza analogs, viz., o-quinonediimines, have received only scant attention (Friedrichsen and Bottcher 1981), the available information on their cycloadditions being mainly concerned with their participation in Diels-Alder reactions with alkenes (Friedrichsen and Schmidt 1978). 

However, the ZnCl2-catalyzed reaction of o-quinoneimine dibenzimide 266a (R = = H) and allylstannane 264 resulted in the formation of ring-allylated 

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The a-bromo-7-lactone 901 undergoes smooth coupling with the acetonyltin reagent 902 to afford the o-acetonyl-7-butyrolactone 903[763j. The o-chloro ether 904, which has no possibility of //-elimination after oxidative addition, reacts with vinylstannane to give the allyl ether 905, The o -bromo ether 906 is also used for the intramolecular alkyne insertion and transmetallation with allylstannane to give 907[764],... 

Evans developed a new method for the synthesis of [(-C-allylglycosides, based on BusSnOTf-mediated ring-opening of glycal epoxides with allylstannanes as nucleophiles [81a], This methodology has been efficiently used in the (3-stereoselective introduction of the side chain (C44-C51) of spongistatin 2 (Scheme 8.43) [81b,c]. 

The indium-mediated allylation carried out with allylstannanes in combination with indium chloride in aqueous medium was reported by Marshall et al.113 Allylindium was proposed as the reaction intermediate. Various aldehydes can be alkylated very efficiently with 3-bromo-2-chloro-l-propene mediated by indium in water at room temperature. Subsequent treatment of the compound with ozone in methanol followed by workup with sodium sulfite provided the desired hydroxyl ester in high yield.114... 

The radical source must have some functional group X that can be abstracted by trialkylstannyl radicals. In addition to halides, both thiono esters and selenides are reactive. Allyl tris(trimethylsilyl)silane can also react similarly.232 Scheme 10.11 illustrates allylation by reaction of radical intermediates with allylstannanes. 

Alkyl halides possessing / -hydrogens are usually poor substrates for carbonylative cross-coupling due to competitive / -hydride elimination/ Allyl chlorides can be used in carbonylative cross-coupling with allylstannanes/ phenyl-, 3-furyl, or vinylstannanes " to afford allylketones in modest to good yields. Divinylketones can be accessed through the reaction of vinylstannanes with vinyl iodides or vinyl triflates, with the latter requiring the addition of LiCl. Synthetic potential of this method has been proved in the formation of macrocyclic ketone jatrophone. In the reaction of vinyl triflates with tetramethyltin or aryltrimethylstannanes the additional activation by ZnCle is required. 

Allylation of Pyranosyl Compounds with Allylstannane [19,20]. A solution of the methyl-(p-D-galactopyranosyl chloride) onate 22 (953.5 mg, 1.8 mmol) in 30 mL of dry, oxygen-free THF, was heated to 60°C. To this solution under nitrogen, were added the tributylallyl tin 23 (5.2 mL, 14.7 mmol) and A1BN (15 mg, 0.1 mmol). After 20 h, the solvent was evaporated, and the residue was taken up in 5 mL of acetonitrile. The acetonitrile layer was extracted with 20 mL of n-hexane and then concentrated. Chromatography on silica gel (toluene-acetone, 4 1) afforded the product 24 (889 mg, 93%), containing two anomers. Nuclear magnetic resonance (NMR) spectroscopy showed a ratio of the two anomers of 1.8 1. 

Asymmetric catalysis of BINOL-Ti complexes in the reaction of aliphatic and aromatic aldehydes with an allylstannane has also been reported independently by Umani-Ronchi [54] and Keck [55]. The former group has suggested that a new complex generated by the reaction of the BINOL-Ti complex with allylstannane is the catalytic species that provides remarkably high enantioselectivity (Scheme 8C.23). It is interesting that no reaction occurs if dry MS 4A... 

Stereo specific generation and reactions of allylic alkali and alkaline earth metals have been reviewed121 and solvent-mediated allylation of carbonyl compounds with allylstannanes has been explored.122 Chiral phosphoramides derived from (5 )-proliiie have been used to catalyse asymmetric allylation of aromatic aldehydes by allylic trichlorosilanes.123... 

As organotin compounds (organostannanes) undergo smooth Pd-catalysed transmetallation, aryl halides react with a wide variety of aryl-, alkenyl- and alkylstannanes [139]. Coupling with allylstannane is the first example [140]. The reaction is called the Migita-Kosugi-Stille or Stille coupling. Aryl, alkenyl, allyl, alkynyl and benzyl... 

The reactions of a-(arylsulfonyl)acetophenones with allylstannane in the presence of AIBN give a nearly 1 1 mixture of allyl tosyl sulfone and the corresponding ketone. NMR studies reveal the generation of tin enolate during the reaction course (Equation (S3)).238... 

Treatment of aldehydes with allylstannane 1 in the presence of BF3 would normally afford branched homoallylic alcohols. Suggest a mechanism... 

Allylalwn. This compound is a useful Lewis acid for activation of electrophiles containing oxygen to allylation with allylstannanes. It is usually more effective than BF3 etherate. ... 

The chiral titanium complex BINOL-T1CI2 also catalyzes the asymmetric carbonyl addition reaction of allylic silanes and stannanes. Thus the addition reaction of glyoxylate with (E)-2-butenylsilane and -stannane proceeds smoothly to give the syn product in high enantiomeric excess (eq 12). The syn product thus obtained can be readily converted to the lactone portion of verrucaline A. The reaction of aliphatic and aromatic aldehydes with allylstannane is also catalyzed by BINOL-TiC to give... 

Umani-Ronchi et al. [56] investigated the asymmetric allylation of aldehydes with allylstannane in the presence of chiral bis(oxazoline) ligands and several metal salts (Sch. 31). Combination of zinc halides and the bis(oxazoline) ligand 70 gave the ally-lated product 71 with moderate enantioselectivity (40 % ee), while other metal salts afforded either no product or racemic products. Because the formation of an allyl-zinc-bis(oxazoline) species was excluded on the basis of the NMR experiments, the reaction was considered to proceed by a Lewis acid-mediated pathway. 

Table 10. Titanium-mediated allylation with allylstannanes.

Although allylation of imines with allylsilanes is encountered less frequently, that with allylstannanes seems more common, probably because of the enhanced nucleo-philicity of the tin reagent compared with the silyl counterpart. Equations (109) [292] and (110) [293,294] illustrate the allylation of imines. In the former reaction, a catalytic amount of the L wis acid, TiCl(OTf)3, is sufficient to bring the reaction to completion. Intramolecular allylation of imines [295] or hydrazones [296] led to the stereoselective construction of amino-cyclic structures, as shown in Eq. (HI) [296]. 

Alkylations. The effect of subjoined Lewis acid (e.g., trimethyl borate) on the catalytic ally lation of aldehydes with allylstannanes promoted by a BINOL-Ti complex has been examined. With allenyltributylstannane the products are homopropargyl alcohols.. Allylation in a Sn(II)-mediated Barbier reaction exhibits much lower ee, although jllenylation with (terminally substituted) propargyltributylstannanes shows good results. 4-Trimethylsilylbut-2-ynyl)tributylstannane undergoes destannylative addition to... 

Allylations, Reaction of a-bromoketones with allylstannanes in the presence of SnCl2 leads to allyl ketones. The new skeletons arise from an in situ rearrangement process (from the bromohydrin derivatives). y-Selective allylation is mediated by the SnClj-CuCl2 system in water-dichloromethane. ... 

Addition to C=0. Hydrates of a-ketoaldehydes react selectively at the aldehyde group with allylsilanes under the influence of YbfOTfjj at room temperature. The allylation of aldehydes with allylstannanes is accelerated by benzoic acid." Another method for the synthesis of homoallylic alcohols is by the ene reaction, thus y,6-unsaturated a-hydroxy esters are obtained from glyoxylic esters at room temperature in a catalyzed process. ... 

There are very few examples of Lewis base-promoted allylations of aldehydes with allylstannanes. In 1992 Baba disclosed an intriguing method for allylation of aldehydes with allyl- and 2-butenyltributylstannanes in the presence of catalytic-amounts of dibutyltin dichloride and certain coactivators such as tetrabutylammo-nium iodide, tributylphosphine oxide, HMPA or tetraphenylphosphonium iodide [76]. No definitive mechanistic information is available on the role of the co-activators the authors speculate that the ligands accelerate the metathesis to form allyldibutyltin chloride which is the actual nucleophile. The same group has recently reported the use of a lead(II) iodide/HMPA catalyst for the allylation of a,yff-epoxyketones [76bj. 

Diastereoselective radical allylations have been studied in many different contexts, and a plethora of information exists regarding stereocontrol in these reactions. Allylations have been performed using the traditional trapping and )9-elimination sequence occurring typically with allylstannanes as well as a stepwise atom transfer/ elimination sequence found to occur with allylsilanes. Stereochemistry is commonly controlled through the use of chiral auxiliaries or by 1,2-induction, and functionalized anh -aldol and amino acid products are available using this established methodology. 

Highly diastereoselective allylations were also achieved in a slightly different manner through radical addition to chiral oxazolidinone acrylate and trapping with allylstannane [25]. In reactions with a,yS-unsaturated substrates, the Lewis acid... 

The reactions of diarylcarbenium ions, Ar2CH+, with allylstannanes are kinetically first order in each reagent and involve irreversible addition to give the cation which is stabilised by the P-stannyl substituent, followed by loss of R3Sn+ (or sometimes attack of a nucleophile at C2).40... 

Pyridines, quinolines,50 isoquinolines,51 and imidazoles52 react with allylstannanes in the presence of acyl halides, via the corresponding (V-acyl salts, to give the l-acyl-2-allyl derivatives of the 1,2-dihydro compounds. 

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