Medicinal leeches use their suction discs for locomotion, adhesion to the host and, in the case of the anterior disc, also for blood ingestion. The biomechanics of their suction-based adhesion systems has been little understood until now. We investigated the functional morphology of the anterior and posterior suckers of Hirudo verbana by using light and scanning electron microscopy. Furthermore, we analysed the adhesion qualitatively and quantitatively by conducting behavioural and mechanical experiments. Our high-speed video analyses provide new insights into the attachment and detachment processes and we present a detailed description of the leech locomotion cycle. Pull-off force measurements of the anterior and posterior suction organs on seven different substrates under both aerial and water-submersed conditions reveal a significant influence of the surrounding medium, the substrate surface roughness and the tested organ on attachment forces and tenacities.
Tertiary Grignard reagents and dibromomethane efficiently cyclopropanate allylic (and certain homoallylic) magnesium and lithium alcoholates at ambient temperature in ether solvents. Lithium (homo)allyl alcoholates are directly cyclopropanated with magnesium and CH2Br2 under Barbier conditions at higher temperatures. The reaction rates depend on the substitution pattern of the (homo)allylic alcoholates and on the counterion with lithium giving best results. Good to excellent syn-selectivities are obtained from alpha-substituted substrates, which are in accord with a staggered Houk model. In tandem reactions, cyclopropyl carbinols are obtained from allyloxylithium or -magnesium intermediates, generated in situ by alkylation of conjugated aldehydes, ketones, and esters as well as from allyl carboxylates or vinyloxiranes. Using this methodology, numerous fragrance ingredients and their precursors were efficiently converted to the corresponding cyclopropyl carbinols.
Cyclopropane derivatives Q 0021Tandem Cyclopropanation with Dibromomethane under Grignard Conditions.-Treatment of allylic and homoallylic alcoholates with CH 2 Br 2 and tBuMgCl allows an efficient access to cyclopropyl carbinols and their homologues. The reaction of α-substituted substrates proceeds with good to high syn-selectivity. One-pot formation of cyclopropyl carbinols form aldehydes, ketones, esters, as well as oxiranes is possible.-(BRUNNER, G.; EBERHARD, L.; OETIKER, J.; SCHROEDER*, F.; J. Org. Chem. 73 (2008) 19, 7543-7554; Richstoff-Forsch., Givaudan AG, CH-8600 Duebendorf, Switz.; Eng.) -Jannicke 08-076
C y c l o p r o p a n a t i o n w i t h D i b r o m o m e t h a n eAbstract: Tertiary Grignard reagents and dibromomethane efficiently cyclopropanate allylic (and certain homoallylic) magnesium and lithium alcoholates at ambient temperature in ether solvents. Lithium (homo)allyl alcoholates are directly cyclopropanated with magnesium and dibromomethane under Barbier conditions at higher temperatures. The reaction rates depend on the substitution pattern of the (homo)allylic alcoholates and on the counterion with lithium giving best results. Good to excellent syn-selectivities are obtained from a-substituted (homo)allyl alcohols. In tandem reactions, cyclopropyl carbinols are obtained from allyloxylithium or -magnesium intermediates, generated in situ by alkylation of conjugated aldehydes, ketones, and esters as well as from allyl esters and carbonates or vinyloxiranes. 1 Scheme 1 OH 1 a OH 2 a (dr = 1:1) CH 2 Br 2 (3 equiv), 10-30 °C, Et 2 O t-BuMgCl (4 equiv), THF, 87% P r o c e d u r e 1 : Deprotonation with t-BuMgCl and cyclopropanation with CH 2 Br 2 P r o c e d u r e 2 : Sequential Grignard addition / cyclopropanation of conjugated aldehydes CHO OH 5 g 2 gPentylMgBr in THF, 0 °C, then CH 2 Br 2 (3 equiv), 10-30 °C, then t-BuMgCl (3 equiv), Et 2 O, 95%
Cyclopropanation with Dibromomethane under Grignard and Barbier Conditions. -Dibromomethane (II) together with a tertiary Grignard reagent cyclopropanate (homo)allylic magnesium and lithium alcoholates efficiently. The cyclopropanation under Grignard conditions afford higher syn-selectivities at ambient or higher temperatures than those obtained by other methods in the case of substrates having substituents in the α-position. Lithium allyl alcoholates provide the best cyclopropanation rates, especially in the case of relatively unsubstituted allyl or sensitive α-tertiary allyl alcoholates or under Barbier conditions. Lithium (homo)allyl alcoholates are cyclopropanated directly with (II) and magnesium under Barbier conditions at higher temperatures, cf. (I)→(VII). In tandem reactions carbinols (X), (XVI), and (XXI) are obtained from allyloxylithium or -magnesium intermediates, generated in situ by alkylation of conjugated aldehydes, ketones, or vinyloxiranes like (VIII), (XIV), and (XIX).
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