Boron-Substituted Building Blocks in Diels-Alder and Other Cycloaddition Reactions

Abstract

Boron-containing building blocks are among the most prominent starting materials in several transformations based on their wide range of synthetic applications. Over the last decade various cycloaddition reactions were reported where boron-containing 1,3-dienes or boron-containing dienophiles were used. Combined with the broad follow-up chemistry, target-oriented as well as diversity-oriented syntheses could be established.

Preparation of 1,3-dienyl organotrifluoroborates and their Diels–Alder/cross-coupling reactions

“…Dienes. We first tried Diels-Alder reactions of diene (27) with N-phenylmaleimide (30) in toluene and ethyl acrylate and methyl vinyl ketone (MVK) in ethanol/methanol and found that boron containing cycloadducts (31-35) could be isolated in high yield. Those cycloadducts could then subsequently be cross coupled using Pd catalysis to yield organic cycloadducts (36)(37).…”

“…Newly formed halo-dienes (43)(44)(45) were first subjected to the protocol (used for formation of the unsubstituted 2-BF 3 diene (27)) to attempt to prepare the corresponding BF 3 -substituted dienes. The first step was to generate the corresponding Grignard reagent followed by addition of trimethoxy borate and quenching by KHF 2 /H 2 O.…”

Synthesis of 2-boryl-1,3-butadienes from tributylphosphine stabilized zirconacyclopropenes and alkynes

“…The yellow oil was obtained in 72% yield and was analyzed by GC/MS, elemental analysis, and NMR spectroscopy. 1 …”

“…While 1-boryl-1,3-butadienes are available by numerous means and are extremely useful intermediates especially in the DielsAlder reaction [1][2][3], the chemistry of the isomeric 2-boryl-1,3-dienes lags in development because of a paucity of general methods available for their synthesis. Among these methods are Carboni's free-radical addition of bromomethane sulfonyl bromide to 2-propenylboronate and subsequent vinylogous RambergBäcklund reaction in 81% yield [4].…”

A novel, efficient synthesis of N-aryl pyrroles via reaction of 1-boronodienes with arylnitroso compounds

“…The reaction of nitroso compounds with dienes is well known, 3 deriving 3,6-dihydro-1,2-oxazines, which have a number of uses, including as bioactives and in synthetic applications. 4 As part of a 25 programme to examine the potential of nitroso-dienophiles and 1-boronodienes 5 for the cascade construction of novel structures, 6 we examined the reaction of dienes 1 with arylnitroso compounds 2 with the expectation of obtaining the oxazines 3 and/or 4 from which cascade reactions could be carried out to access allylic 30 alcohols 5 and/or 6 (Scheme 1).…”