Horizontal gene transfer among nitrogen-fixing bacteria in the guts of termite Coptotermes gestroi

Efficient synthesis and subsequent transformations of phenylsulfanylbicyclo[2.2.2]octenones and phenylselenylbicyclo[2.2.2]octenones

Inverse-electron-demand Diels-Alder reactions of masked o-benzoquinones 2 with phenyl vinyl sulfide and phenyl vinyl selenide furnished highly functionalized bicyclo[2.2.2]octenone derivatives 3 and 4, respectively, in excellent regio- and stereoselectivities and yields up to 90%. The bicyclo[2.2.2]octenone derivatives 3 with the sulfur functionality were subjected to an oxidation-elimination process to furnish bicyclo[2.2.2]octadienone systems 7 in good yields. During the reduction process, the Diels-Alder adducts 3e and 4e led to 8, whereas the carbon-centered radicals generated from the other adducts 3a-d and 4a-d provided various rearranged products 9-13 depending on the substitution pattern and reagents utilized (Raney-Ni or n-Bu(3)SnH). Surprisingly these radicals showed preference for the carbonyl functionality to the olefinic double bond, leading to interesting rearrangement reactions of mechanistic importance and possible synthetic utility. Interestingly the alcohols obtained from the reduction of Diels-Alder adducts 3a-d underwent desulfurization smoothly to give desulfurized products in high yields; thus a detoured method of "reduction-desulfurization-oxidation" provides an entry to desulfurized bicyclo[2.2.2]octenones without rearrangement.

Molecular complexity from aromatics: a novel, stereoselective route to tricyclo[5.2.2.0(1,5)]undecenones, tricyclo[6.2.2.0(1,6)]dodecenones, and [n.3.3]propellanes

A general stereoselective route to functionalized and substituted tricyclo [5.2.2.0(1,5)]undecenones, tricyclo[6.2.2.0(1,6)]dodecenones, and [3.3.3]- and [4.3.3]propellanes from simple aromatic precursors is reported. The methodology involves generation and cycloaddition of annulated cyclohexa-2,4-dienones with various acrylates followed by manipulation of the resulting tricyclic adducts, leading to functionalized tricyclo[5.2.2.0(1,5)]undecenones and tricyclo[6.2.2.0(1,6)]dodecenones endowed with a beta,gamma-enone chromophore. Photochemical reaction of the tricyclic chromophoric systems followed by reductive cleavage provided an efficient entry into propellanes.