Face-selective Diels–Alder reactions of (1R,5R)-3-formyl-6,6-dimethylbicyclo[3.1.1]hept-3-en-2-one

Abstract

The stereofacially differentiated enone aldehyde 11 was chosen to study the effects of steric and electronic influence on the Diels–Alder reaction. Under Lewis acid catalysis, 11 adds to dienes at low temperatures at a reasonable rate. Yields of desired chiral adducts are good to high with zinc chloride and boron trifluoride etherate catalysis. In all cases only products of addition to the Re face of general type 27 were observed. The regiochemistry of the adducts is exclusively that predicted by the ortho and para rules. The stereochemistry shows a very high selectivity in favour of aldehyde-endo transition state products. Unusual byproducts were also obtained in some examples and mechanisms of these unexpected reactions are discussed.

β-Pinene and camphor based, pyrazole-tethered triarylphosphines as chiral P,N ligands for palladium

“…Synthesis of (-)-β-pinene based pyrazole ligand (L1) began with commercially available (-)-β-pinene of >98% optical purity. It was oxidised by NaIO4-RuO4 to afford (+)-nopinone A 30 , which was formylated using a reported procedure 31 to obtain the product B. Condensation of the 1,3-dicarbonyl compound B with 2bromophenylhydrazine afforded the pyrazole derivative C. Lithium-halogen exchange followed by quench with PPh2Cl furnished the desired ligand L1 in 31% overall yield from (-)-β-pinene (Scheme 1). Camphor was similarly converted to acyl derivatives E 32 and F that were condensed with 2-bromophenyl hydrazine to afford the pyrazole nuclei G and H. Lithium-bromine exchange followed by treatment with PPh2Cl yielded the desired optically active ligands L2 and L3.…”

“…Column chromatography was performed with silica gel 230 ~ 400 and 100 ~ 200 meshes. All 1 H NMR (300 and 500 MHz), 13 C NMR (75 and 125 MHz), 31 P NMR (212 MHz) and 19 F NMR (470.5 MHz) spectra were recorded in CDCl3 solution and reported in ppm (δ). X-ray single crystal data were collected using MoKα (λ = 0.7107 Å) radiation on a SMART APEX II diffractometer equipped with CCD area detector.…”

α-Activated Cross Conjugated Cycloalkenone Systems in Organic Synthesis

“…In contrast to enone ester 29, studies on the stereoselective outcome of the corresponding enone aldehyde 32 in Diels-Alder reaction were also carried out [18]. The results revealed that the yields of adduct 33 were extremely catalyst dependent, and better yields were obtained only when mild Lewis acids such as zinc chloride was employed (Scheme 14).…”

Catalysis of the Diels-Alder Reaction by Organotin Halides

“…However, Carlson and coworkers 8 found limited Diels-Alder catalytic activity for a number of tin(II) and tin(IV) halides. Likewise, tin(IV) chloride was not an effective catalyst for a Diels-Alder reaction with a stereofacially differentiated enone 9 . We wish to report catalysis of the Diels-Alder reaction by organotin halides containing one or more tin atoms.…”