Effect of steric bulk on the absolute reactivity of allene oxides.
Alpha-alkyl substituted fluorenylidene allene oxides were generated photochemically from appropriately substituted fluorenol derivatives in 2,2,2-trifluoroethanol (TFE) in order to assess the affect of steric bulk on the absolute reactivity of the allene oxides. The absolute reactivities of the allene oxides were measured using nanosecond laser flash photolysis, and were found to change little in TFE upon going from alpha-methyl to alpha-butyl to alpha-t-butyl. However, all three alpha-alkyl substituted allene oxides were considerably more reactive than the alpha-hydrogen derivative, indicating that steric bulk did not result in a decrease in reactivity as is typically found in other allene oxides. The contrary reactivity of the fluorenylidene allene oxides is explained by examining in detail the reactions of these allene oxides, determined from product studies.
Stereoselektive Bildung von Halbacetalen des cis‐2,3‐Dimethylcyclopropanons aus 2‐Halogen‐3‐pentanonen. [4 + 3]‐Cycloadditionen an konjugierte Dien‐Systeme
2-Chlor- und 2-Brom-3-pentanon (1,2) reagieren in Methanol, Ethanol und 2-Propanol mit den entsprechenden Natriumalkoxiden hochstereoselektiv zu Halbacetalen des cis-2,3-Dimethylcyclo-propanons (4aα–4cα). Das Benzoat von 4aα wurde durch Rontgenstrukturanalyse charakterisiert. cis-2,3-Dimethylcyclopropanon kann durch Aldoladdition mit Malonsaure-dimethylester abgefangen werden. Es erleidet eine disrotatorische retro-elektrocyclische Ringoffnung zu einem W-konfigurierten Allylium-2-olat (Oxallyl) 10, welches hochstereoselektive [4 + 3]-Cycloadditionen mit Isopren, (E)-1,3-Pentadien, Furan und 2-Methylfuran eingeht. Mit Methanol und 2,2,2-Trifluorethanol entstehen die 2-Alkoxy-3-pentanone. N-Methylpyrrol wird in 2-Stellung oxoalkyliert. 
 
 
 
Stereoselective Formation of cis-2,3-Dimethylcyclopropanone Hemiacetals from 2-Halo-3-pentanones. — [4 + 3] Cycloadditions with Conjugated Diene Systems 
 
 
 
2-Chloro- and 2-bromo-3-pentanone (1, 2) react in methanol, ethanol, and 2-propanol with the corresponding sodium alkoxides in a highly stereoselective manner to provide the hemiacetals of cis-2,3-dimethylcyclopropanone (4aα – 4cα). The benzoate of 4aα was characterized by an X-ray crystal structure determination. cis-2,3-Dimethylcyclopropanone can be trapped by an aldol type addition with dimethyl malonate. It undergoes a disrotatory retro-electrocyclic ring opening to form a W-configured allylium-2-olate (oxyallyl) 10 which combines with isoprene, (E)-1,3-pentadiene, furan, and 2-methylfuran in highly stereoselective [4 + 3]cycloadditions. With methanol and 2,2,2-trifluoroethanol, the 2-alkoxy-3-pentanones are formed. N-Methylpyrrol is oxoalkylated at the 2-position.
Genotypic diversity in field isolates of Babesia bovis from cattle with babesiosis after vaccination.
OBJECTIVE
To determine whether particular genotypes of Babesia bovis were common to field isolates obtained from cattle properties in Queensland where the B bovis vaccine had apparently failed.


DESIGN
A comparative study of polymerase chain reaction genotypes in different populations of B bovis.


PROCEDURE
Two polymerase chain reaction assays were applied to analyse DNA extracts of B bovis vaccine (K, T and Dixie strains) and 27 field isolates from 24 properties where disease outbreaks had occurred despite the use of the vaccine. To evaluate the stability of the genotypes identified, 11 of the field isolates were inoculated into experimental cattle that had either been previously vaccinated with T strain or not vaccinated.


RESULTS
No particular genotype of B bovis was responsible for the problems observed in previously vaccinated herds. None of the isolates had genotypes identical to the vaccine strains used. No geographic trends among the genotypes were observed. Isolates that originated from the same property also had different genotypes. Blood passage of the 11 field isolates in either previously vaccinated or nonvaccinated cattle did not alter the original genotype.


CONCLUSION
No particular genotypes identified by the Bv80 and BvVA1 polymerase chain reaction assays could be associated with vaccine failures.