A Novel Pentose Synthesis via Palladium(II)-Catalyzed Cyclization of an Unstable Hemiacetal

Synthesis of Polyoxygenated Heterocycles by Diastereoselective Functionalization of a Bio-Based Chiral Aldehyde Exploiting the Passerini Reaction

“…However, starting from the pseudoenantiomeric monobutyrate of 2, obtained by enzymatic monohydrolysis of the corresponding dibutyrate [5], 14 could be synthesized as well. In this case, the olefination gave best results simply treating the aldehyde with the anion of triethyl phosphonoacetate, affording E-18 in almost diastereomerically pure form [23].…”

“…The starting building block 9 is cheap and renewable. Initially we planned to synthesize aldehyde 7 (Scheme 1) bearing a terminal double bond (R 3 = H) [23] and for this purpose we submitted 2 to Swern oxidation followed by Wittig olefination, but, under a variety of conditions, we never succeeded to get 12 (Scheme 3). Initially we planned to synthesize aldehyde 7 (Scheme 1) bearing a terminal double bond (R 3 = H) [23] and for this purpose we submitted 2 to Swern oxidation followed by Wittig olefination, but, under a variety of conditions, we never succeeded to get 12 (Scheme 3).…”

“…The starting building block 9 is cheap and renewable. Initially we planned to synthesize aldehyde 7 (Scheme 1) bearing a terminal double bond (R 3 = H) [23] and for this purpose we submitted 2 to Swern oxidation followed by Wittig olefination, but, under a variety of conditions, we never succeeded to get 12 (Scheme 3). Then we switched to the carbethoxymethylenation which has the advantage of introducing two functional groups at once (a double bond conjugated with an ester), which could have enabled exploring different post-condensation transformations after the multicomponent reaction.…”

“…In order to suppress the Michael cyclization, we decided to substitute the acetyl with a protecting group that could be cleaved under acidic conditions, such as the t-butyldimethylsilyl ether. It was easily introduced through a high-yield, epimerization-free protection-deprotection sequence affording 17 [23]. Of course, this sequence produces ent-14.…”

“…((4R,5S)-5-(((tert-butyldimethylsilyl)oxy)methyl)-2,2-dimethyl-1,3-dioxolan-4-yl)methanol(17). It was prepared in two steps from 2, as previously described, as a pale yellow oil in 98% overall yield[23].R f = 0.60 (PE:Et 2 O 1:1). [α] 23 D = +3.73 (c = 1.03, CHCl 3 ).…”