Osamu Yonemitsu

A general and convenient synthetic method of geometrically pure (Z)-1-bromo-1-alkenes

Abstract Palladium catalyzed hydrogenolysis of 1,1-dibromo-1-alkenes by tributyltin hydride proceeds smoothly to give ( Z )-1-bromo-1-alkenes with excellent stereoselectivity in good yields. Dibromomethylenation of aldehydes by a combination of CBr 4 and Ph 3 P in methylene chloride and the successive hydrogenolysis affords ( Z )-1-bromo-1-alkenes in one-pot.

Facile chelation-controlled reductive opening of methoxybenzylidene acetals with Bu3SnH and MgBr2. Regioselective protection strategy as MPM ethers

Abstract A mild and efficient regioselective reductive opening of methoxybenzylidene acetals using a combination of Bu 3 SnH and MgBr 2 ·OEt 2 , mainly via five-membered chelation intermediates is described. This reaction was applied to synthetic intermediates of myriaporon and tedanolide.

Stereocontrolled Synthesis of (11Z)-Retinal and Its Analogues

Suzuki coupling of stereochemically pure (Z)-bromotetraene 1-which is extremely unstable but can be kept in frozen benzene in the presence of a small amount of PPh3 at &sminus 01;20°C-and (Z)-alkenylboronic acid 2 provides the stereocontrolled synthesis of (11Z)-retinal 3. The 11Z configuration, which is introduced by selective catalytic debromination of the corresponding dibromo precursor of 1, is retained in this step. TBDMS = tBuMe2 Si.

Total synthesis of 16-membered tetraene macrolide hygrolidin

Abstract The first total synthesis of 16-membered tetraene macrolide antibiotic hydrolidin, a potent and relatively specific inhibitor of the vacuolar ATPases, has been achieved, incorporating macrolactonization by the modified Yamaguchi method and fragment assembly aldol reaction to establish the C17-C18 bond as key steps.

Synthetic studies of halichondrin B, an antitumor polyether macrolide isolated from a marine sponge. 8. Synthesis of the lactone part (C1C36) via horner-emmons coupling between C1C15 and C16C36 fragments and Yamaguchi lactonization

Abstract The lactone part ( 2 ) of halichondrin B ( 1 ) was synthesized by Yamaguchi macrolactonization of the seco-acid ( 3 ), which was synthesized via coupling of C1C15( 4 ) with C16C36 ( 5 ), prepared through stereoselective construction of the E ring starting from C16C26 ( 7 ) and C27C36 ( 8 ).

Stereoselective Synthesis of the C(1)−C(12) Fragments of Tedanolides − Application of a syn-Selective Tin(II)-Mediated Aldol Reaction and a Convertible Methoxybenzyl Protecting Group

Stereoselective synthesis of two C(1)−C(12) fragments, 3 and 4, of antitumor agents tedanolide (1) and 13-deoxytedanolide (2) was achieved by means of several regio- and/or stereoselective reactions. Ethyl ketone 14 was synthesized from methyl (S)-3-hydroxy-2-methylpropionate (16a) by way of a Weinreb amide. A highly syn-selective tin(II)-mediated aldol reaction between 14 and aldehyde 15, prepared from (R)-propionate 16b, proceeded smoothly, and subsequent reduction gave diol 13, which was transformed into 3, incorporating a C(3),C(5)-MP acetal moiety, by taking advantage of convertible MPM protecting groups. Another fragment, 4, with C(3)-O-methyl and C(5)-O-MPM groups, was also synthesized. A crucial step was the selective transformation of C(2),C(3)-diol 21 into C(2)-O-TBS, C(3)-O-Me compound 22.

Tridentate pyridine podand ionophores exhibiting perfect Ag+ ion selectivity

Abstract A new type of podand ionophores was prepared, in which three pyridine moieties were appropriately arranged for tridentate Ag + complexation. They well discriminated Ag + ion from Pb 2+ , Cu 2+ , Co 2+ , Zn 2+ and Ni 2+ ions and mediated selective and efficient transport of Ag + ion.

Reactions and synthetic applications of β-oxo-sulphoxides. Part VI. A new synthesis of the pyrido[4,3-b]carbazoles olivacine and ellipticine

The acid-catalysed cyclization of β-oxo-sulphoxides was applied to a synthesis of olivacine and ellipticine. An oxo-sulphoxide derived from methyl N-benzylindole-3-propionate was cyclized with trifluoroacetic acid to give a 2-oxo-1,2,3,4-tetrahydrocarbazole derivative, and a side chain was introduced at the carbonyl group. Aromatization and construction of the pyridine ring proceeded efficiently to yield olivacine. In the same way, ellipticine was synthesized from methyl N-benzylindole-3-butyrate.

A Facile Preparation of Geometrically Pure Alkenyl, Alkynyl, and Aryl Conjugated Z-Alkenes: Stereospecific Synthesis of Bombykol

Abstract Ni- and Pd-catalyzed cross coupling reactions of 2-alkenyl, 2-alkynyl, and 2-aryl substituted (1Z)-1-bromoalkene with alkyl Grignard reagents gave 1-alkyl substituted (1Z,3E)-diene, (1Z)-en-3-yne, and (1Z)-2-arylethene, each in good yield. When (trimethylsilyl)methylmagnesium chloride was used as the Grignard reagent, conjugated Z-allylsilane was produced. Bombykol, (10E,12Z)-10,12-hexadecadien-1-ol, a sex pheromone of female moss, Bombyx mori, was synthesized stereospecifically.

Toward the total synthesis of hygrolidin: Stereocontrolled construction of the C1–C17 seco-acid fragment and the C18–C25 masked hemiacetal subunit

Abstract Toward the first total synthesis of 16-membered macrolide antibiotic hygrolidin, the C1C17 seco-acid fragment and the C18C25 masked hemiacetal subunit as potential precursors have been synthesized in enantiomerically homogeneous forms.