ON THE JAPANESE SPECIES OF VICARYA

1. The genus Vicarya was established by D\u27ARCHIAC and HAIME upon Nerinea? verneuili D\u27ARCHIAC, a Miocene species from India.2. Discussions as to the generic value of Vicarya and as to its generic position have been given by K. MARTIN, W. H. DALL, W. D. SMITH, K. A. V. ZITTEL and recently by T. TAKEYAMA. Its position is now placed in the Potamidinae.3. The following forms are now considered as valid in the genus Vicarya, namely, ecocenica, verneuili, callosa, callosa japonica, callosa martini, callosa yokoyamai, yatuoensis and probably callosa semperi.4. Vicarya is a genus having species restricted in geographical distribution to the Far East, and ranging in time from the Eocene to Miocene, being best developed in the Lower or Middle Miocene, a time prior to its extinction which may be Upper Miocene, according to the usage of the term.5. In the Japanese Miocene are found the following forms, namely, callosa japonica, callosa yokoyamai, callosa martini and yatuoensis ; all are restricted to the Middle Miocene of Japan, and play an important role in the geological history and stratigraphical relationships of geographically isolated geological formations.6. The manuscript genus Vicaryella of T. TAKEYAMA is here defined and thus made valid ; the following species are now found to belong here, namely, tyosenica the genotype, nipponica, bacula and probably ishiiana.7. The habitat of both Vicarya and Vicaryella was one of brackish-water, at very shallow depths such as at the tidal zone, of warm water and particular nature.8. From the associated faunules of both Vicarya and Vicaryella, it is found that their stratigraphical importance is nearly equal.9. Keys to the species of both genera have been given in order to faciliate workers along this line.10. Descriptions and figures of all known species of both genera are given

A novel bifunctional allyldisilane as a triple allylation reagent in the stereoselective synthesis of trisubstituted tetrahydrofurans

Three for the price of two: A bifunctional allyldisilane undergoes a two-step triple allylation sequence with pairs of aldehydes to give all-cis trisubstituted tetrahydrofurans in excellent enantio- and diastereoselectivity (see scheme). The first allylation step, which sets up the key stereogenic

New pyridine N-oxides as chiral organocatalysts in the asymmetric allylation of aromatic aldehydes

Asymmetric allylation of aromatic aldehydes 1 with allyltrichlorosilane (2) can be catalyzed by new terpene-derived bipyridine N,N'-dioxides 12-15 and an axially chiral biisoquinoline dioxide 17b with good enantioselectivities. Dioxides have been found to be more reactive catalysts than their monooxide counterparts. Crown Copyright . All rights reserved

On the mechanism of asymmetric allylation of aldehydes with allyltrichlorosi lanes catalyzed by QUINOX, a chiral lsoquinoline N-oxide

Allylation of aromatic alclehydes 1a-m with allyl- and crotyl-trichlorosilanes 2-4, catalyzed by the chiral N-oxide QUINOX (9), has been found to exhibit a significant dependence on the electronics of the aldehyde, with p-(trifluoromethyl)benzaldehyde 1g and its p-methoxy counterpart 1h affording the corresponding homoallylic alcohols 6g,h in 96 and 16% ee, respectively, at -40 degrees C. The kinetic and computational data indicate that the reaction is likely to proceed via an associative pathway involving neutral, octahedral silicon complex 22 with only one molecule of the catalyst involved in the rate- and selectivity-determining step. The crotylation with (E) and (Z)-crotyltrichlorosilanes 3 and 4 is highly diastereoselective, suggesting the chairlike transition state 5, which is supported by computational data. High-level quantum chemical calculations further suggest that attractive aromatic interactions between the catalyst 9 and the aldehyde 1 contribute to the enantiodifferentiation and that the dramatic drop in enantioselectivity, observed with the electron-rich aldehyde 1h, originates from narrowing the energy gap between the (R)- and (S)reaction channels in the associative mechanism (22). Overall, a good agreement between the theoretically predicted enantioselectivities for la and 1h and the experimental data allowed to understand the specific aspects of the reaction mechanism