A Straightforward Organocatalytic Alkylation of 2‐Arylacetaldehydes: An Approach towards Bisabolanes

Abstract

A highly stereoselective organocatalytic aalkylation of 2-arylacetaldehydes with a commercially available carbenium tetrafluoroborate is described. The stereoselective alkylation was carried out in acetonitrile/water, under air in the presence of a commercially available imidazolidinone (MacMillans catalyst). Key intermediates for the synthesis of bisa-bolanes were obtained through a simple chemistry. In particular a direct, enantioselective and facile synthesis of (R)-(À)-curcumene is described. Scheme 4. Reaction sequence for the synthesis of the key intermediates 13a-k. 530 Scheme 6. Synthesis of the iodides 16a-k. Scheme 7. Elongation by two carbons via reaction of iodides 16a-e with malonate ion and successive decarboxylation. Scheme 8. Published synthetic routes to bisabolanes starting from ester 18c.532

A Versatile Organocatalytic Approach for the Synthesis of Enantioenriched gem‐Difluorinated Compounds

“…We have investigated the gem ‐difluorination by preparing suitable substrates by using our protocols for organocatalytic alkylations 21. A different methodology was employed in respect to our first communication 16d. The new protocol uses commercially available MacMillan catalyst 20 as the monohydrochloride salt without adding any base.…”

From QCA (Quantum Cellular Automata) to Organocatalytic Reactions with Stabilized Carbenium Ions

“…[107] This organocatalytic alkylation was applied to the total synthesis of arundic acid, [102] Lilial, [108] and Bisabolans (Scheme 16). [109] We are now trying to apply the benzodithiolylium approaches for addressing the challenges connected to the synthesis of the dehydropropionate chain. [110] In particular, we are interested in controlling the introduction of many methyl groups, with the correct absolute configuration and relative configuration in the 1,3-, 1,4-, and 1,5-positions on an alkyl chain, by a reproducible and iterative process.…”

“…No dried solvents or strong bases are necessary for the alkylation, and the procedure can be successfully used by undergraduate students 107. This organocatalytic alkylation was applied to the total synthesis of arundic acid,102 Lilial,108 and Bisabolans (Scheme ) 109…”

Iodine-mediated rearrangements of diallylsilanes

“…7,8 For instance, iodide 10 could be alkylated with dimethylmalonate providing silyl diester 11 in 76% yield (Scheme 6). 13 Cross-metathesis of 10 with methyl acrylate using the 2 nd generation Grubbs’ catalyst ( Ru-II ) gave 12 in very high yield. 14 Compound 12 was then taken on to the silylmethyl-functionalized pyrrolidine 13 upon treatment with benzylamine which was isolated in 64% yield (85% based on recovered starting material).…”