The clinical success
of α,α-difluorocyclopropanes,
combined with limitations in the existing synthesis portfolio, inspired
the development of an operationally simple, organocatalysis-based
strategy to access cis-configured derivatives with
high levels of stereoselectivity (up to >20:1 cis:trans). Leveraging an I(I)/I(III)-catalysis platform
in the presence of an inexpensive HF source, it has been possible
to exploit disubstituted bicyclobutanes (BCBs) as masked cyclobutene
equivalents for this purpose. In situ generation
of this strained alkene, enabled by Brønsted acid activation,
facilitates an unprecedented 4 → 3 fluorinative ring contraction,
to furnish cis-α,α-difluorinated cyclopropanes
in a highly stereoselective manner (up to 88% yield). Mechanistic
studies are disclosed together with conformational analysis (X-ray
crystallography and NMR) to validate cis-α,α-difluorocyclopropanes
as isosteres of the 1,4-dicarbonyl moiety. Given the importance of
this unit in biology and the foundational no → π*
interactions that manifest themselves in this conformation (e.g.,
collagen), it is envisaged that the title motif will find application
in focused molecular design.
Vocatives play an important role for establishing and maintaining social contacts in human communication. Given the functional and formal diversity in their culture-specific realisation, this study, based on two spoken corpora of everyday conversations in Spanish and German, compares the use of different types of vocatives in these two languages, especially from a pragmatic and sociolinguistic point of view. Firstly, we present a brief review on the communicative functions of vocatives and describe the tertium comparationis, the methodology and the corpora used for this study. Then, we compare the frequency of Spanish and German vocatives in different conversational settings. What emerges is greater tendency to use vocatives in the Spanish data, especially for reinforcing social contact within the conversations. As far as the variation of vocative-forms is concerned, this contrastive analysis reveals different pragmatic and sociolinguistic functions of last-name-vocatives, endearment-terms and the use of the pronouns
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