Caste-specific tyramides from Myrmicine ants.

Analysis of the extracts of male ants of Monomorium minimum and Monomorium ebeninum by GC-MS and GC-FTIR revealed the presence of tyramides 2 and 4c, for which the structures were established by comparison with synthetic samples. These compounds and their analogues 1 and 3 were also found in males of other Monomorium species, males of Myrmicaria opaciventris, and males of several Solenopsis (Diplorhoptrum) species. Vapor-phase FTIR spectra revealed critically important structural clues to two of the tyramides, which had methyl branching in the tyramide acyl moiety. Tyramide 4c exhibited a strong intramolecular amide NH hydrogen bond where an alpha-keto group was deduced to be present in the acyl moiety and also showed the overlap of this ketone group frequency with that of the amide nu(C horizontal lineO). The biological function of these compounds is uncertain; however, their role in ant-mating behavior may be suggested by a large body of evidence.

Advances in Lewis acid controlled carbon-carbon bond-forming reactions enable a concise and convergent total synthesis of bullatacin.

Lewis acids control regioselectivity in the alkylation of epi-chlorohydrin and the stereochemistry of an alkyne addition to set the C24/C23 anti relationship. These advances facilitate an efficient total synthesis of bullatacin in 13.3% overall yield from commercial starting materials.

Selective oxidation of zirconocyclopentenes via organoboranes.

[reaction: see text] A new, convenient, one-pot protocol is described for oxidation of zirconocyclopent-2-enes selectively at the sp(3) carbon by efficient transfer to electrophilic ((c)Hex)(2)BCl followed by oxidation with H(2)O(2)/NaOH to afford 1-alkylidene-2-hydroxymethylcyclopentanes. Results with several substrates show that overall reaction efficiencies for the zirconocene-mediated enyne cyclization, boron transmetalation, and oxidation sequence are generally comparable to yields obtained from protonation of intermediate zirconocycles. The formation of E/Z olefin isomers from the cyclization-oxidation sequence and an acid-catalyzed pinacol-type rearrangement of a vinylsilane are described.