Homoallylic hydroxy ketones

Allylation of a-hydroxy ketones.1 An allyltrifluorosilane and triethylamine (1 1) react with a-hydroxy ketones in refluxing THF to form tertiary homoallyl... 

In 1989, Sakurai et al. reported that allyltrifluorosilanes react with a variety of a-hydroxy ketones in the presence of stoichiometric amount of triethylamine to yield the corresponding tertiary homoallylic alcohols in an extremely high regio-and diastereoselective manner10 (Scheme 3.2h). Upon reacting with a-hydroxy acetone, the (L )-crotylsilane 4E gave 6-syn as a major product in 83% yield with... 

The unsaturated linkage in enantiomerically pure a-methyl-. -y-unsaturated ketones (45) exerted a powerful stereochemical influence on their reduction with L-selectride, particularly when R is a tri-methylsilyl group. The anti homoallylic alcohols (46) were produced with uniformly excellent stereoselectivity (>93 7) via a Felkin transition state in which the double bond occupied the perpendicular position (equation 12). This Felkin selectivity was sufficient to overcome any chelation-mediated contribution in the reduction of a-vinyl-p-hydroxy ketones (47) to the, 2-syn diols (48) with LiEtsBH in THF at -78 °C (equation 13).58... 

Allylation andaldol reaction. Diallylstannane and silyl enol ethers condense with carbonyl compounds to furnish homoallylic alcohols and p-hydroxy ketones, respectively. A mixture of HjO, EtOH, and toluene is a suitable reaction medium as CufOTflj is stable in water. 

Dias et al. reported that the oxidation of Al-Boc-protected homoallylic alcohols with OsOq as a catalyst in the presence of NalOq efficiently occurred in Et20 H20 (1 1) to provide 4-N-Boc-amino-3-hydroxy ketones in high yields (eq 73). ... 

Storage Moisture-sensitive store in cool, dry place away from heat, sparks, open flame store under nitrogen keep tigthly closed Uses Reducing agent in silylation-reduction-allylation sequence of p-hydroxy esters to homoallylic-substituted 1,3-diols, in silylation-hydrosilation-oxidation of allyl alcohols to 1,3-diols, reduction of p-hydroxy ketones to anti-1,3 diols... 

The Pd(Quinox)Cl2, (Quinox = 2-(2-quinolyl)-4,5-dihydrooxazole) catalysed Wacker-type oxidation of olefins bearing homoallylic alcohols by TBHP led to the corresponding /3-hydroxy ketones in good yields. Since the oxidation was catalyst controlled, it was significantly faster than the substrate-controlled Tsuji-Wacker oxidation. The bis- and fra-homoallylic alcohols were oxidized to cyclic peroxyketals, presumably via nucleophilic attack of the methyl ketone. Kinetics of the Wacker-type oxidation of olefins by TBHP in the presence of Quinox (ligand), and (54) as the catalyst reveal first-order dependence on ligand and olefin, and rate saturation in TBHP, as expected of the proposed mechanism (Scheme 9)... 

The 4-hydroxy-1-alkene (homoallylic alcohol) 81 is oxidized to the hetni-acetal 82 of the aldehyde by the participation of the OH group when there is a substituent at C3. In the absence of the substituent, a ketone is obtained. The hemiacetal is converted into butyrolactone 83[117], When Pd nitro complex is used as a catalyst in /-BuOH under oxygen, acetals are obtained from homoallylic alcohols even in the absence of a substituent at C-3[l 18], /-Allylamine is oxidized to the acetal 84 of the aldehyde selectively by participation of the amino group[l 19],... 

The synthesis of 11 jS-hydroxy-A -3-ketones (17) from A ° -compounds (16) has been carried out by the homoallylic hydroxyl-assisted Simmons-Smith reaction. 

If the reaction is conducted with allylic bromides or a-bromoesters in acetonitrile containing aldehydes or ketones, homoallylic alcohols11 (Equation 8.15) or (3-hydroxy esters12 are respectively obtained. 

Gallium-mediated allylation of aldehydes or ketones in water gives the corresponding homoallyl alcohols in high yields without the assistance of either acids or sonication. The diastereoselectivity of the allylation of 2,3-dihydroxy-propanal depends on the solvent. When the reaction is carried out in water, the dominant product is the yy/z-isomer. In contrast, the anti-isomer is dominant when THF is employed. The yy/z-isomer may be regarded as the chelation-controlled product, due to the hydrogen bond between the two hydroxy groups. The aqueous environment favors... 

As described in the sections above, it is well established that reactions of Lewis acid-activated aldehydes and ketones with silyl enolates afford -hydroxy or /7-sil-oxy carbonyl compounds (Mukaiyama aldol reactions). Occasionally, however, ene-type adducts, that is /-siloxy homoallyl alcohols, are the main products. The first example of the carbonyl-ene reaction of silyl enolates was reported by Snider et al. in 1983 [176]. They found that the formaldehyde-MesAl complex reacted smoothly with ketone TMS enolates to give y-trimethylsiloxy homoallyl alcohols in good yield. Yamamoto et al. reported a similar reaction of formaldehyde complexed with methylaluminum bis(2,6-diphenylphenoxide) [177]. After these early reports, Kuwajima et al. have demonstrated that the aluminum Lewis acid-promoted system is valuable for the ene reactions of several aldehydes [178] and for-maldimine [179] with silyl enolates bearing a bulky silyl group. A stepwise mechanism including nucleophihc addition via an acyclic transition structure has been proposed for the Lewis acid-promoted ene reactions. 

The intramolecular Mannich reaction has been combined with the facile [3,3] sigmatropic rearrangement of iminium cations to provide a versatile synthesis of 3-acylpyrrolidines and other more complex ring systems containing this subunit.In the simplest case, a homoallylic amine with alkoxy or hydroxy substitution at the allylic site is allowed to react with an aldehyde in the presence of an equivalent or less of acid to yield substituted 3-acylpyrrolidine products (Scheme 50). The mild conditions of this transformation—which occurs at near ambient temperature and neutral pH—are apparent in the success of this sequence with labile aldehydes such as furfural. Ketones can be employed also in this case a two-step... 

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