Reductive Cleavage of 5,6-Dihydro-2H-pyran Derivatives; Facile Synthesis ofcis-3-Hexenol

Pd(OAc)2/Ph3P-catalyzed dimerization of isoprene and synthesis of monoterpenic heterocycles

“…In a first instance, the synthesis of pyranes by a hetero-Diels–Alder reaction was realized. Thus, the reaction of 2-TT with formaldehyde in acetic acid at reflux led after 6 h exclusively to one regioisomer dihydropyrane 5 in 64% ( Scheme 3 , left) [ 42 ]. Next, the thermal Diels–Alder reaction with maleic anhydride and N -substituted maleimides in toluene provided a ready access to the fused ring-system 6a–c in excellent yields (81–91%; Scheme 3 , middle).…”

[(p‐Cymene)RuCl2]2: An Efficient Catalyst for Highly Regioselective Allylic Alkylations of Chelated Amino Acid Ester Enolates

“…The racemic precursors for the other esters 5 , were prepared by addition of vinylmagnesiumbromide to the corresponding aldehyde. The ( Z )‐configured alcohol required for the ( Z )‐substrates ( Z )‐ 4 c and ( Z )‐ 4 d was obtained by ether cleavage of 2,5‐dihydrofuran29 and the ( E )‐isomer was obtained by reduction of ( E )‐crotyl ethyl ester 30. The racemic allylic alcohols were converted into the benzoates, acetates, carbonates, and phosphates by standard methods.…”

Contemporary Synthetic Strategies towards Secosteroids, abeo-Steroids, and Related Triterpenes

“…With 15 in hand, the selective cleavage of the C19-O bond eventually could be realized under Birch conditions (Li in ethylamine) to give the corresponding hydroxy moiety at C3 and with concomitant removal of the acetate group as well as the reductive removal of the C22ketal (see structure 16) in 21% yield over the five steps. 11 Chemoselective oxidation of both primary hydroxy groups in triol 16 using 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) and N-chlorosuccinimide (NCS), followed by protection of the remaining secondary alcohol as a triethylsilyl ether, then furnished dialdehyde 17. All that remained to complete the synthesis of cyclocitrinol was the oxidative deformylation of both aldehyde groups 12 followed by installation of the required side chain.…”

“…Our synthesis 28 started once again from literature known i-steroid enone 32, 19 which, upon treatment with 2iodoxybenzoic acid (IBX), underwent desaturation 29 and led to the introduction of the desired Δ 9 (11) bond along with concomitant desaturation of the C14 and C15 positions (see structure 47). The undesired Δ 14 bond was selectively reduced with L-Selectride yielding 1,3-diene 48, which was transformed into endoperoxide 49 in a [4+2]-cycloaddition with 1 O 2 .…”

“…Schiglautone A (8) (Figure 3) is part of the Schisandra triterpenoid family and was isolated in 2011 from Schisandra glaucenscens. 66 The structure of 8 features a cyclohexylfused bicyclo[6.4.1]tridecene carbon skeleton with an unusual Δ 9 (11) alkene and six stereocenters, three of which are quaternary. Biosynthetically, it has been proposed that 8 originates from anwuweizic acid (structure not shown) by a series of rearrangements and oxidation events.…”