Isao Kadota

Stereocontrolled intramolecular cyclization of ω-tributylstannyl ether aldehydes. synthesis of the 6·7·7·6 ring system of polycyclic ethers

Abstract The BF 3 .OEt 2 mediated intramolecular cyclization of the γ-oxo-substituted allylic tin ( 1 ) having an aldehyde group at the terminus of the carbon chain proceeded in a stereocontrolled manner to give the 7-membered β-hydroxy cyclic ether ( 2a ) with high diastereoselectivity. This method was applied for the synthesis of the 6·7·7·6 ring system ( 3a ).

Cyclic transition state in the acid catalyzed intramolecular allylstannane-aldehyde condensation

Abstract Brφnsted acid catalyzed or Bu 4 NF-TiCl 4 mediated cyclization of (Z)-ω-stannyl ether aldehyde 1a gives 2a , whereas (E)-isomer 1b affords 2b . To explain this stereochemical outcome, a push mechanism is proposed.

Syntheses of the AB and EFGH ring segments of gambierol

Abstract Stereocontrolled syntheses of the AB and EFGH ring systems of gambierol ( 1 ) are described. The two key intermediates 3 and 55 , representing the AB and EFGH ring frameworks, were prepared from 2-deoxy- d -ribose via linear sequences. Browns asymmetric allylboration and the intramolecular hetero-Michael reaction were successfully applied to the construction of the A ring moiety. Synthesis of the EFGH ring segment 55 was achieved by the SmI 2 mediated reductive cyclization, constructing the EF ring bearing two 1,3-diaxial methyl groups, and the palladium catalyzed coupling of enol triflate and zinc bishomoenolate, making the GH ring moiety. Attempted convergent approaches toward the EFGH ring framework are also described.

Synthesis of the J ring segment of gambieric acid

Abstract The J ring segment 2 of gambieric acid was synthesized stereoselectively by the coupling between the cyclic ether component 3 and the alkenyl iodide 4 . The tetrahydropyran 3 was stereoselectively synthesized by the 6- endo -cyclization of a hydroxyepoxide prepared from deoxy- d -ribose. The side chain moiety 4 was prepared by the stereoselective hydrostannation of an internal alkyne.

Synthesis of the AB ring system of gambierol

Abstract Synthesis of the AB ring system of gambierol ( 1 ) was achieved from 2-deoxy- d -ribose. The key steps were the stereoselective allylation of the aldehyde 6 , corresponding to the B ring, and the intramolecular hetero-Michael reaction of 9 .

Asymmetric total syntheses of hydroxylated piperidine alkaloids via the intramolecular reaction of γ-aminoallylstannane with aldehyde

Abstract Asymmetric total syntheses of (+)-desoxoprosopinine and (−)-desoxoprosophylline were accomplished using L-glutamic acid as the chiral source, in which the intramolecular reaction of a γ-aminoallylstannane with an aldehyde was used as a key step.

Concise synthesis of cyclic ethers via the palladium-catalyzed coupling of ketene acetal triflates and a zinc homoenolate. Synthesis of the DE and GH ring segments of gambierol

Abstract Concise syntheses of the DE and GH ring segments of gambierol ( 1 ) were achieved by the palladium-catalyzed coupling of ketene acetal triflates and a zinc homoenolate, followed by the hydroboration of the resulting cyclic enol ethers and subsequent lactonization.

A novel convergent approach to trans-fused polyether frameworks based on the reaction of vinylstannanes and triflates and its application to a synthetic study of the EFGH ring system of gambierol

Abstract A new strategy for the convergent assembly of six-membered polycyclic ether ring fragments has been developed based upon the novel reaction between vinylstannanes with triflates in the presence of a strong base. The application of the present method has allowed for a synthetic study of the EFGH ring of gambierol to be achieved.

A general and efficient method for the preparation of γ-alkoxyallylstannanes via an acetal cleavage

Abstract The reaction of various alcohols and γ-methoxyallylstannane 3 in the presence of a catalytic amount of CSA afforded mixed acetals in high yields. The treatment of the acetals with TMSI and HMDS produced γ-alkoxyallylstannanes in high yields via elimination of methanol.

Total synthesis of (+)-desoxoprosopinine via the intramolecular reaction of γ-aminoallylstannane

Abstract A stereoselective total synthesis of (+)-desoxoprosopinine starting from L-glutamic acid as a chiral source was accomplished, in which the intramolecular reaction of γ-aminoallylstannane with aldehyde was used as a key step.