Keiji Tanino

Highly threo-selective ene-reaction of 2-(alkylthio)allyl silyl ethers with aldehydes

Abstract Under the influence of Mc2A1C1, ene-reaction of 2-(alkylthio)allyl silyl ethers readily proceeds with a wide range of aldehydes to afford the corresponding γ-hydroxy carbonyl compounds as their enol silyl ethers with high threo-preference as well as excellent (Z)-selectivity.

Ene reaction of 2-(alkylthio)allyl silyl ether involving a chirality transfer.

Abstract A highly enantio-selective ene reaction was developed on the bases of charility transfer. Under the influence of Me 2 AlCl, the reactions of various aldehydes with ( S )-3-( tert -butyldimethylsiloxy)-2-(ethylthio)-1-butene which was easily prepared from ( S )-ethyl lactate afforded the optically active adducts in high ee.

Lewis acid promoted ene-like reactions of enol ethers with aldehydes

Abstract Use of organoaluminum reagents induces ene-like reactions of enol silyl ethers with aldehydes, and enols having bulky silyl groups selectively afforded syn adducts.

Highly stereoselective chelation controlled ene-reaction of 2-(alkylthio)allyl silyl ethers

Abstract Under the chelation conditions the title compounds reacted with α-benzyloxyaldehyde to afford syn diol exclusively. Further, three contiguous diastereomeric centers were constructed with high stereoselectivity by using ( E ) or ( Z )-crotyl silyl ether. This methodology was applied to the stereoselective synthesis of brassinolide side chain.

METHYLENECYCLOPENTANE ANNULATION VIA FORMAL 3 + 2 CYCLOADDITION REACTION

Abstract A new method for methylenecyclopentane annulation via formal [3+2] cycloaddition reaction was developed. Under the influence of Lewis acids, enol ethers and vinylsulfides were treated with I-(alkylthio)-2-(trimethylsilylmethyl)allyl esters 1a or 1b to afford methylenecyclopentanes in good yields. The reaction proceeds with almost complete regioselectivity as well as high stereoselectivity.

HIGHLY EFFICIENT METHOD FOR CORIOLIN SYNTHESIS

Abstract Formal total synthesis of coriolin has been accomplished on the basis of a [3+2] cycloaddition reaction of a vinylsulfide with 3-(methylthio)-2-siloxyallyl cation. A five-membered vinylsulfine as a C ring unit was prepared in five steps from commercially available compounds. The first [3+2] cycloaddition reaction gave the BC ring intermediate, which was then converted into a bicyclic vinylsulfide in three steps. The construction of the A ring by the second [3+2] cycloaddition reaction followed by two-step-conversion afforded the tricyclic enone (30% overall yield from isobutyronitrile) which has previously been synthesized and converted into coriolin.

3-(Alkylthio)-1,2-bis(siloxy)-3-butenes as efficient chirality transferred building blocks

Abstract In the presence of Me 2 AlCl, reactions of the title compounds with a variety of aldehydes proceeded with high efficacy of chirality transfer to give the corresponding optically pure ene adducts, which could be converted to the γ-lactones, e.g., rove beetle pheromone.

A selective one-carbon ring expansion reaction of 1-siloxycyclo-alkanecarbaldehydes catalyzed by a lewis acid

Abstract Under the influence of a Lewis acid, 1-siloxycycloalkanecarbaldehydes undergo one-carbon ring enlargement reaction to afford the corresponding 2-siloxycycloalkanones in good yields. Regiochemistry of this rearrangement reaction has also been examined, and use of FeCl 3 greatly improves the selectivity to give the product arising from migration of a more-substituted site.

Silicon-based nucleophile mediated one-carbon ring expansion reaction of 1-(trimethylsilylmethyl)cycloalkanecarbaldehydes

Abstract Under the influence of an appropriate Lewis acid, TMS sulfide and TMS-OTf induced one carbon ring expansion of 1-(trimethylsilylmethyl)cycloalkanecarbaldehydes to afford the corresponding 2-methylenecycloalkyl sulfides and ethers, or their isomerized ones in good yields.

A highly efficient method for one-carbon ring expansion. Preparation of 1-alkoxy-2-methylenecycloalkanes

Abstract ZnBr 2 induces a facile one-carbon ring expansion of 1-(TMS-methyl)-cycloalkanecarbacetals to yield the corresponding 1-alkoxy-2-methylenecycloalkanes, whereas a similar transformation can be performed efficiently from the parent aldehydes under the influence of TMS-OTf (1 mol%) and TMS-OMe (2 equiv).