Synthesis of 10‐deazariboflavin and related 2,4‐Dioxopyrimido[4,5‐b]quinolines

The reduction of tosylhydrazones and of acyl tosylhydrazides

The apparent and the real: What looks like a Friedel-Crafts alkylation reaction of electron-deficient pyrroles is actually a Pd(II)-catalyzed, norbornene-mediated C-H activation reaction, in which the alkylation of the pyrrole core occurs by reductive elimination. As well as ethyl-1H-pyrrole-2-carboxylate, several other 2,3-disubstituted pyrroles underwent the selective C5 alkylation in good yield.

Palladium-catalyzed direct C-H alkylation of electron-deficient pyrrole derivatives.

An account of the total synthesis of celogentin C is presented. A right-to-left synthetic approach to this bicyclic octapeptide was unsuccessful due to an inability to elaborate derivatives of the right-hand ring. In the course of these efforts, it was discovered that the mild Braslau modification of the McFadyen−Stevens reaction offers a useful method of reducing recalcitrant esters to aldehydes. A left-to-right synthetic strategy was then examined. The unusual Leu−Trp side-chain cross-link present in the left-hand macrocycle was fashioned via a three-step sequence comprised of an intermolecular Knoevenagel condensation, a radical conjugate addition, and a SmI2-mediated nitro reduction. A subsequent macrolactamization provided the desired ring system. The high yield and concise nature of the left-hand ring synthesis offset the modest diastereoselectivity of the radical conjugate addition. Formation of the Trp−His side-chain linkage characteristic of the right-hand ring was then accomplished by means of a...

John S. McFadyen

Papers

128. A new method for the conversion of acids into aldehydes