trans‐Tetrahydrofurans by OH‐Assisted Ru‐Catalyzed Isomerization of 2‐Butene‐1,4‐diols

Abstract

We herein report a general method for the synthesis of 1,2‐annulated trans‐tetrahydrofurans by the OH‐assisted Ru‐catalyzed isomerization of (Z)‐2‐butene‐1,4‐diols (using Chaudret's catalyst), followed by reduction of the incipient lactol (using Et3SiH and Amberlyst 15). Alternatively, the lactol can be oxidized to the corresponding lactone (using Ikariya's catalyst). It was shown by labeling experiments that an addition/elimination pathway is (at least to some extent) operative for the isomerization reaction.

Well-defined transition metal hydrides in catalytic isomerizations

“…Labelling and cross-over experiments were consistent with an intermolecular addition/ elimination mechanism. 39 B. Allylic amines and amides. During the early development of the industrially-relevant isomerization of allylic amines, a cobalt hydride catalyst [HCo(N 2 )(PPh 3 ) 3 ] was first employed.…”

One-pot synthesis of (−)-Ambrox

“…Stoll completed the synthesis of Ambrox for the first time by the reduction of sclareolide with LiAlH 4 , followed by an acid-catalysed cyclization of the resulting diol to produce (−)-Ambrox 7 . Several other synthetic routes were reported to prepare Ambrox starting with natural terpenoids 8 9 . For commercial syntheses, the major starting materials investigated included homofarnesic acid, homofarnesol, monocyclohomofarnesic acid, sclareol and monocyclohomofarnesol 10 11 12 13 .…”

A Concise Synthesis ofrac‐Ambrox®viathe Palladium(0)‐Catalyzed Carboalkoxylation of an Allylic Ammonium Salt, as Compared to a Formaldehyde HeteroDiels–AlderApproach

“…Thus, when δ-pyronene 3 was used (Scheme 2), the [4 + 2] cycloaddition afforded a 9:1 mixture of regioisomers 8 and 16 7 in 66 % yield of crude product. Regioisomer 8 could be isolated pure in 38 % yield by CC/SiO 2 , while Birch reduction of a 8:2 mixture of 8/ 16 8 gave the reported minor homo-allylic alcohol 18, [48][49][50] which was subsequently cyclized to afford the bicyclic ether 19 [51,52] in 69 % yield as a 83 : 17 trans/cis mixture. 9 The analogous cycloaddition performed on diene 4 afforded again, essentially, the undesired regioisomer β-12 in 25 % yield of isolated product.…”