TiCl4-n-Bu4NX (X = I, Br, and Cl) combination-induced coupling of alpha,beta-unsaturated ketones with aldehydes

A green procedure for the synthesis of cinnamate esters using Aliquat®336

As an effective solid-liquid phase-transfer catalyst as well as an ionic liquid medium Aliquat® 336 has been applied in the synthesis of cinnamate esters under mild green chemistry procedures involving microwave irradiation.

Intramolecular Morita-Baylis-Hillman reaction as a strategy for the construction of tricyclic sesquiterpene cores

Starting from a common polyfunctionalized bicyclo[3.2.1]octane-6,8-dione intermediate, a concise synthetic route to tricyclic cores found in quadrane, suberosane, cedrane and related sesquiterpenes was developed using a Morita-Baylis-Hillman intramolecular reaction as a key step.

Highly diastereoselective access to polyfunctionalized 1,3-oxazines promoted by Brønsted/Lewis acids

The Brønsted/Lewis acid catalyzed reaction of α-alkyloxyamides tethered to α,β-unsaturated ketones (aldehydes) afforded exclusively polyfunctionalized 1,3-oxazines with high diastereoselectivities and in high yields.

Manganese-catalyzed ring-opening chlorination of cyclobutanols: regiospecific synthesis of γ-chloroketones

An efficient, mild, and practical ring-opening chlorination of cyclobutanols is developed by means of manganese catalysis.

Efficient Baylis-Hillman reactions of cyclic enones in methanol as catalyzed by methoxide anion

The Baylis-Hillman reactions of cyclic enones with a variety of aldehydes were investigated. 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) was found to be a viable catalyst in promoting the reactions of sterically retarded substrates in methanol. The reactions showed clear solvent dependence and only occurred in hydroxylic solvents, especially in methanol. Further consideration on the steric character of DBU and its high basicity jointly with other experimental observations suggests that the methoxide anion should be the "true" Baylis-Hillman catalyst. This has been confirmed by the effectiveness of similar reactions directly employing methoxide as the catalyst. The reaction pathways of this type of catalysis are proposed to depend on the choice of substrates. Supporting experimental observations were demonstrated and discussed in relation to mechanistic considerations. This study also reveals that both DBU and sodium methoxide can be successfully applied as effective catalysts in methanol to promote the Baylis-Hillman reactions for a range of cyclic enones including cyclopent-2-enones, cyclohex-2-enones, gamma-pyrone, and 1-benzopyran-4(4H)-ones.

MgI2-catalyzed halo aldol reaction: a practical approach to (E)-beta-iodovinyl-beta'-hydroxyketones

A novel generation of 1-iodo-3-siloxy-1,3-butadienes has been developed by reacting trimethylsilyl iodide (TMS-I) with alpha, beta-unsaturated ketones in dichloromethane at 0 degrees C without the use of any catalyst. The halo aldol reaction of these butadiene intermediates with aldehydes was efficiently carried out by using magnesium iodide as the catalyst. Twelve beta-iodo-alpha,beta-unsaturated-beta'-hydroxyketones (halo aldols) have been synthesized under the new condition with excellent geometric selectivity and good chemical yields (>80% chemical yields for 11 examples).

Ring-opening reactions of methylenecyclopropanes promoted by metal halides

The methylenecyclopropanes (MCPs) react with various metal chlorides or bromides to give the corresponding homoallylic chlorides or bromides in good yields. [reaction: see text]

Asymmetric halo aldol reaction (AHA)

[reaction: see text] The asymmetric halo aldol reaction (AHA) using Evans oxazolidinones as chiral auxiliaries has been established for tandem I-C/C-C bond formations. The new asymmetric reaction provides a practical approach to a variety of halo aldols of a non-Evans type that cannot be easily synthesized by other methods. Excellent diastereoselectivity (>95%) and yields (80-93%) have been obtained for eight examples.

TiCl4-Promoted Baylis−Hillman Reactions of Substituted 5-Isoxazolecarboxaldehydes with Cycloalkenones1

The Baylis-Hillman (BH) reaction of substituted 5-isoxazolecarboxaldehydes with cyclohexenone in the presence of TiCl(4) invariably lead to the formation of hemiacetals beside the BH adducts. A similar reaction in the presence of DABCO, DBU, or 3-HQN yielded minor quantities of phenols in addition to the usual BH adducts. Similar to 5-isoxazolecarboxaldehydes, the TiCl(4)-mediated BH reaction of cyclohexenone with various benzaldehydes also furnishes hemiacetals in considerable yields. The reaction mechanism involving the formation of alpha-chloromethyl enone as an intermediate has been proposed. The synthesis of hemiacetals 5 and 14 from compound 4 in the presence of cyclohexenone and cyclopentenone, respectively, under acidic conditions indicates that enolization and aromatization of the cyclohexene ring are the key steps in the reaction mechanism.