A Boron Alkylidene–Alkene Cycloaddition Reaction: Application to the Synthesis of Aphanamal

Abstract

We describe an unusual net 2+2 cycloaddition reaction between boron alkylidenes and unactivated alkenes. This reaction provides a new method for construction of carbocyclic ring systems bearing versatile organoboronic esters. In addition to surveying the scope of this reaction, we provide details about the mechanistic underpinnings of this process, and examine application to the synthesis of the natural product aphanamal.

Versatile cobalt-catalyzed regioselective chain-walking double hydroboration of 1,n-dienes to access gem-bis(boryl)alkanes

“…For example, different reactivity of the two boryl groups in gembis(boryl)alkanes allows stepwise functionalization of their two C-B bonds [8][9][10] . Interestingly, gem-bis(boryl)alkanes can generate two types of carboanions, monoboryl-or gem-bis(boryl)-functionalized carboanions, via deprotonation by LiTMP (lithium tetramethylpiperidide) or alkoxide-induced deborylation 11,12 . Over past decades, series of catalytic reactions have been developed to access these gem-bis(boryl) compounds [13][14][15][16][17] , such as double hydroboration of alkynes [18][19][20] , diborylation of alkenes 21,22 , hydroboration of 1-borylalkene [23][24][25] , or C-H borylation reactions [26][27][28][29] .…”

Cobalt‐Catalyzed Diborylation of 1,1‐disubstituted Vinylarenes: A Practical Route to Branchedgem‐Bis(boryl)alkanes

“…As an important class of organoboryl compounds, gem ‐bis(boryl)alkanes can undergo a wide range of organic transformations. For example, the carboanions generated from gem ‐bis(boryl)alkanes in the presence of bases can selectively react with a variety of electrophiles, such as alkylhalides, N‐heteroaromatic N‐oxides, alkenes, and carbonyls . In addition, gem ‐bis(boryl)alkanes can undergo various metal‐catalyzed cross‐coupling reactions, such as arylation and vinylation, allylic substitution, alkylation, epoxide ring‐opening, and 1,2‐addition of imines and carbonyl groups .…”

Generation of α‐Boryl Radicals and Their Conjugate Addition to Enones: Transition‐Metal‐Free Alkylation of gem‐Diborylalkanes

“…First, in the presence of metal alkoxide bases, a-borylc arbanion speciesc an be generated via deborylative pathway,w hich can be subsequently trapped by variouse lectrophiles, leading to the formation of diverse alkyl boronates (Scheme 1a). [3] Alternatively, with the aid of lithium amide bases, diborylalkane carbanion species can be obtained via deprotonative pathway and react with variouse lectrophiles for the synthesis of complex gem-diborylalkane derivatives (Scheme 1b). [2d,e,i,j, 4] However,t ot he best of our knowledge the reactionm ode of gem-diborylalkanes based on radicalp rocess, such as the radical deborylative pathway shown in Scheme 1c, remains unknown in the literature.…”