Birch Reductions at Room Temperature with Alkali Metals in Silica Gel (Na₂K-SG(I))

Abstract

Alkali metals in silica gel (the Na(2)K-SG(I) reagent) cleanly effect Birch reductions of substrates with at least two or more aromatic rings. The reaction conditions are alcohol-free, ammonia-free, and achieve excellent yields and high selectivities at room temperature.

Enantioselective Enzymatic Naphthoyl Ring Reduction

“…Conjugated systems may only be obtained from a base‐catalyzed rearrangement of non‐conjugated Birch products . Though the Birch reduction is a basic and widely used method, the harsh conditions have motivated the search for alternative alkali‐ or ammonia‐free procedures . Furthermore, the radical mechanism excluded the development of stereoselective Birch‐derived methods for naphthoyl‐ring reductions.…”

“…[6] Though the Birch reductioni sabasic andw idely used method,t he harsh conditions have motivated the search for alternative alkali-or ammonia-free procedures. [7] Furthermore, the radical mechanism excluded the development of stereoselective Birch-derived methodsf or naphthoyl-ring reductions.Enzymatic alternatives for the Birch reduction have first been discoveredi na naerobic bacteria that degradem onocyclic aromatics. Here, benzoyl-coenzyme A( CoA) reductases reducet heir substratet oaconjugatedc yclic 1,5-dienoyl-1-carboxyl-CoA, probablyi naBirch-like mannerv ia radicali ntermediates.B enzoyl-CoAr eduction is either ATP-dependenta nd accomplished at a[ 4Fe-4S]c luster,o rp roceeds ATP-independently at am etallo-organic W-cofactor.…”

Catalytic Hydrogenation with Frustrated Lewis Pairs: Selectivity Achieved by Size‐Exclusion Design of Lewis Acids

“…[23] The generality of these catalytic processes is frequently hampered by the lack of selectivity: for example, the hydrogenolysis of aryl-halogen bonds on the carbocyclic ring. As a complementary and alternative method, borohydrides, [24] reducing metals, [25] Hantzsch esters, [26] and silane [27] -based reducing agents were utilized to accomplish the reduction. These transformations often furnish higher functional-group tolerance; however, they are not atom economic and generate a large amount of waste.…”

Reductive N–O cleavage of Weinreb amides by sodium in alumina and silica gels: synthetic and mechanistic studies

“…21 The relative yields of products and over-reduced compounds vary somewhat from run-to-run, apparently due to batch-to-batch differences in the Na-AG reagent, rather than variations in the methodology used. For example, three reductions run side-by-side with the same reagents and concentrations gave essentially the same product yields.…”

“…Na-AG and Na-SG are commercially available free-flowing powders that are powerful reductants and are non-pyrophoric in dry air. [19][20][21] Other advantages are that many of their reductions can be run under ambient conditions and that the environmentally benign spent reducing agent can be removed by simple filtration. In this Letter, we explore both the modest range of applicability of such reagents for WA reduction, and some mechanistic issues raised by these studies.…”