No abstract

We investigated responses of rice plant to three rare sugars, d-altrose, d-sorbose, and d-allose, due to establishment of mass production methods for these rare sugars. Root growth and shoot growth were significantly inhibited by d-allose but not by the other rare sugars. A large-scale gene expression analysis using a rice microarray revealed that d-allose treatment causes a high upregulation of many defense-related, pathogenesis-related (PR) protein genes in rice. The PR protein genes were not upregulated by other rare sugars. Furthermore, d-allose treatment of rice plants conferred limited resistance of the rice against the pathogen Xanthomonas oryzae pv. oryzae but the other tested sugars did not. These results indicate that d-allose has a growth inhibitory effect but might prove to be a candidate elicitor for reducing disease development in rice.

Dark red crystals of the halogen-substituted cyclotrigermenes [(tBu3Si)3Ge3X; X = Cl, Br, I] were obtained in good yields by the reaction of [(tBu3Si)3Ge3]+.TTFPB- (TTFPB- = tetrakis(2,3,5,6-tetrafluorophenyl)borate) with potassium halides (KCl, KBr, or KI) in diethyl ether. The crystal structures of the halogen-substituted cyclotrigermenes reveal a cis-bent Ge=Ge double bond, caused by the introduction of the electronegative halogen atom on the sp3 germanium atom of cyclotrigermene. In solution, an intramolecular halogen migration over the three-membered ring skeleton was observed. Facial stereoselectivity in the Diels-Alder reaction of new cyclotrigermenes with 2,3-dimethyl-1,3-butadiene is also reported.

The heavier group 14 element cation cluster compound, [(tBu3Si)6Ge10I]+.TTFPB- (3+. TTFPB-; TTFPB- = tetrakis(2,3,5,6-tetrafluorophenyl)borate), was unexpectedly obtained by thermolysis of in situ prepared iodocyclotrigermene, (tBu3Si)3Ge3I, in toluene in the presence of KI and K+.TTFPB-. The molecular structure of 3+.TTFPB- has been unambiguously determined by X-ray crystallography, showing that 3+ is a free germyl cation. The three "naked" cationic germanium atoms in the framework constitute a three-center two-electron (3c-2e) bond with a trishomocyclotrigermenylium character, which is well-supported by a theoretical calculation on the model compound Ge10H7+.

A lithium-halogen exchange reaction occurs when the chloro[bis(diisopropylamino)] cyclopropenium tetrafluoroborate salt 1 (X = BF 4 ) is treated with n-butyllithium. The resulting cyclopropenylidene-lithium adduct 3 has been isolated in 45% yield. In the solid state, this compound exists as a polymeric chain with an overall stoichiometry of two LiBF 4 per carbene ligand. Addition of 12-crown-4-ether does not liberate the carbene from the lithium cation, but affords a monomeric tertiary complex (60% yield) that includes the crown ether. Moreover, complex 3 can also be synthesized by depro tonation of the bis(diisopropylamino)cyclopropenium tetrafluoroborate salt 2 (X = BF 4 ) with n-butyllithium, whereas using potassium bis(trimethylsilyl)amide the free cyclopropenylidene was isolated in 53% yield. These results as whole seem to demonstrate that only certain counteranions allow for the isolation of cyclopropenylidene-lithium adducts, and only bases not containing lithium allow for the isolation of the free cyclopropenylidene. The former and the latter presumably prevented Weiss and Yoshida from isolating what would have been the first example of a stable carbene-lithium adduct and a free carbene, respectively. KeywordsCarbenes; cyclopropenylidene; Li; Complex In the 1950s, Breslow[1] and Wanzlick [2] realized that the stability of a carbene could be dramatically enhanced by the presence of amino substituents, but they were unable to isolate a "monomeric" carbene.[3] It was only in 1991, three years after the isolation of a (phosphino) (silyl)carbene,[4] that a bottle-able diamino carbene, namely an imidazol-2-ylidene, was prepared.[5] Even more strikingly, in a paper entitled "1,2,3,4-Tetraphenylimidazol-2-ylidene: The Realization of Wanzlick's Dream", Arduengo [6] reported that a modification of the experimental procedure published by Wanzlick's group makes it possible to isolate one of the exact same carbenes postulated in 1970. [7] Wanzlick was not the only one to nearly isolate the first stable carbene. Indeed, in the 1970s, Yoshida [8] and Weiss [9] attempted independently the preparation of the bis (diisopropylamino)cyclopropenylidene 4 (Fig. 1). Recently, we isolated the exact same carbene (4) after deprotonation of cyclopropenium salt 2 (X = BPh 4 ) with potassium bis(trimethylsilyl) amide.[10] Among the routes used by Yoshida and Weiss were lithium-halogen exchange from 1 (X = ClO 4 )[9a] and the deprotonation of 2 (X = ClO 4 ),[8a,b] both with n-BuLi. However, they were not able to isolate the resulting product. Initially, Yoshida claimed the successful synthesis of the free cyclopropenylidene 4,[8a] but several years later he[8b-e] and Weiss ** We are grateful to the NIH (R01 GM 68825) and Rhodia for financial support of this work, and to the JSPS for a Fellowship to Y. I.