A facile procedure for acetalization under aprotic conditions

BF(3)-Induced rearrangement of aziridino cyclopropanes derived from 2-phenylsulfonyl 1,3-dienes. Application to the total synthesis of (+/-)-ferruginine

Total synthesis of the alkaloid (+/-)-ferruginine (1) has been developed via the 2-phenylsulfonyl 1,3-diene approach. BF(3)-induced rearrangement of the N-protected cyclohexane aziridino cyclopropane 8, derived from its corresponding epoxy cyclopropane, afforded the desired tropane alkaloid skeleton 9 in good yield. Michael addition of nitroethane (as an acyl anion equivalent) and transformation of the nitro group of the adduct 10 to a keto function gave 11. Elimination of benzenesulfinic acid and subsequent replacement of the tosyl group by a methyl group afforded the title compound 1.

Synthesis and structure of 4-O,6-O-glycosylidene glycosides

Interglycosidic spiro ortho esters (9-20) were efficiently prepared from methyl 2,6-di-O-benzylgluco- or galactopyranoside and various sugar lactones in the presence of methoxytrimethylsilane and a catalytic amount of trimethylsilyl triflate. All of the prepared sugar ortho esters possess perhydrospiro[2H-pyran-2,2'-pyrano[3,2-d][1,3]dioxin] ring systems commonly in their molecules and, remarkably, were afforded as single isomers. The configurations of the spiro centers in their molecules were determined or estimated by X-ray single crystallographic analysis and molecular modeling studies. By comparing the conformations of prepared ortho esters, we revealed that the difference in the stability between two possible isomers was principally caused from that between the spiro ring systems in their molecules in each case.

Asymmetric synthesis of (-)-tetrahydrolipstatin: an anti-aldol-based strategy

A stereoselective synthesis of (-)-tetrahydrolipstatin is described. The synthesis involves an asymmetric ester derived titanium enolate anti-aldol reaction, a nitro-aldol reaction to append the C-2' C(11) side chain, and a diastereoselective reduction of a beta-hydroxy ketone to an anti-1,3-diol functionality followed by its elaboration to (-)-tetrahydrolipstatin.

3-Bromopentadienylsilane: A new reagent for the introduction of a functional pentadienyl unit with fixed configuration

The (Z)-1-trimethylsilyl-3-bromopenta-2,4-diene 3 was prepared through a sequence involving the reductive silylation of butadiene, dibromocarbene addition on the resulting disilane 1, and thermolytic ring opening. With aldehydes, this new pentadienylsilane reacts exclusively via an S(E)' ' pathway. In the presence of an alcohol or a carbamate under Lewis acid activation, 3 yields, respectively, bromopentadienyl ethers or bromopentadienyl-protected amines.

Synthesis and inotropic activity of hydroindene derivatives

A synthetic approach to hydroindenic inotropic agents has been developed, starting from enantiopure Hajos-Parrish (1). Hajos-Wiechert (2), and related diketones. Their transformation into C-1 formyl derivatives and other subsequent synthetic targets is described. The results of the thermodynamic equilibration between both epimers of each formyl derivative are analysed. The inotropic activities of selected compounds on right and left atrial preparations are also evaluated and discussed.

Studies on the Mechanism of Action of 2-Formyl-4-pyrrolidinopyridine: Isolation and Characterization of a Reactive Intermediate

This paper describes the mechanism of action of 2-formyl-4-pyrrolidinopyridine (FPP, 1a) which is a catalyst for the hydroxyl-directed methanolysis of alpha-hydroxy esters. This species was initially designed to act as a nucleophilic catalyst; however, we have ruled out a nucleophilic mechanism by examining the activity of 6-substituted-FPP derivatives. These compounds are more hindered in the vicinity of the pyridine nitrogen than FPP itself but are also more active catalysts. Furthermore, the presence of p-nitrophenol, a mild acid, was found to accelerate the catalytic reaction. These results are inconsistent with a nucleophilic catalysis mechanism. We provide evidence that the reaction instead proceeds via dioxolanone intermediate 10. Dioxolanone 10 can be obtained by treating either the p-nitrophenyl ester or the pentafluorophenyl ester of glycolic acid with FPP in chloroform in the absence of methanol. It has been isolated, characterized, and shown to be kinetically competent when subjected to the conditions of the catalytic reaction.

Furan-Terminated N-Acyliminium Ion Initiated Cyclizations in Alkaloid Synthesis

A study of the utility of furan-terminated N-acyliminium ion initiated cyclizations for the synthesis of linearly fused alkaloid precursors (Figure 2) is presented. The outcome of the cyclization event depends on the position of furan tether attachment (2 vs 3), tether length, and furan 5-substituent (R = H, CH(3), Ar). 3-Substituted furans cyclized to form 6- and 7-membered ring containing furans 35-38, 50, and 51 in good to excellent yields. 2-Substituted furans closed to form only 6-membered rings; however, the products obtained were a function of the furan 5-substituent. The 5-H furans 17 and 18 led exclusively to the corresponding furans 21 and 22, while the 5-CH(3)-furans 42 and 43 gave only diketone containing compounds 44 and 45. 5-Arylfurans 66-71 provided mixtures of furan- and diketone-containing products 72-83, with the ratio related to the substitution on the phenyl moiety. A preparation of epilupinine 10 is also discussed.

A simple method for coupling aldehydes to solid support

A new method for attaching aldehydes to solid supports has been developed employing a 2,2-bis(hydroxymethyl)propionic acid (DMPA) functionalized resin. High loading levels are obtained for both aryl and alkyl aldehydes protected as their respective acetals. Treatment of the derivatized resin with 95% TFA then cleanly affords the recovered aldehyde in high yield.

Designed Chiral Acyl Radical Equivalents. Preparation and Cyclizations of Disymmetrically Substituted 1,3-Dioxabicyclo[4.4.0]decan-2-yl Radicals

The diastereoselectivity of 5-exo-trigonal cyclizations of 2-(4-penten-1-yl)-1,3-dioxolan-2-yl and 2-(4-penten-1-yl)-1,3-dioxan-2-yl radicals is investigated. When dioxolanes or dioxanes derived from C(2) symmetrically substituted diols are employed the diastereoselectivity is poor. In the dioxanyl series this is a consequence of the cyclization occurring through a twist-boat conformer. Disymmetrically substituted dioxanyl radicals, derived from the alcohols 21 and 41, are, however, constrained to chairlike conformations and accordingly give rise to highly diastereoselective cyclizations. Conditions are described for the hydrolysis of the resulting spiroacetals and for determination of the ee of the resulting 2-methylcyclopentanones.