Catalytic asymmetric synthesis of Secondary (E)‐allyl alcohols from acetylenes and aldehydes via (1‐alkenyl)zinc intermediates. Preliminary Communication

Abstract

lO.XIT.9 I ) Hydroboration of aliphatic 1-alkynes with freshly prepared dicyclohexylborane (1 mol-equiv., hexane), treatment of the resulting [(E)-1-alkenyl]boranes 5 with Et'Zn or Me,Zn (1.05 mol-equiv.) followed by addition of (-)-3-exo-(dimethylamino)isoborneol (DATB, 8; 0.01 mol-equiv.), subsequent addition of a solution of an aromatic or aliphatic aldehyde (1 mol-equiv., hexane). and quenching with aq. NH,CI provided (E)-ally1 alcohols 6 usually in 713-950/0 yield with 79-98% enantiomeric excess (Scheme 3 and Tuble).Optically pure secondmy ally1 alcohols 3b (as well as their antipodes) are key intermediates in organic synthesis. Recently, we have presented a new enantioselective approach to compounds of the type 3b based on 'asymmetrically catalyzed' additions of (l-alke-ny1)zinc reagents l a [l] and Ib [2] to aromatic and aliphatic aldehydes (Scheme I)').We now envisaged an analogous ligand-controlled 1 -alkenyl transfer from mixed (1-alkenyl)(alkyl)zinc reagents such as Ic focussing our attention on the following points: 1 ) good accessibility, 2) chemical and stereochemical stability'), 3 ) exclusive transfer of S( /lr,nlc I

Catalytic Asymmetric Generation of (Z)-Disubstituted Allylic Alcohols

“…[5][6][7]4 Other drawbacks to the KR include the need to separate the desired allylic alcohol from the epoxy alcohol product and a maximum yield of 50%. 20 More efficient methods to prepare allylic alcohols include asymmetric vinylation of aldehydes [21][22][23][24][25]13,15,[8][9][10][26][27][28] or ketones 29,30 (Scheme 2) and reductive coupling of alkynes and carbonyl compounds. 31-36 These methods simultaneously generate the C-C bond and a stereogenic center in a single step.…”

A novel stereoselective synthesis of (2Z)‐2‐arylsulfanylallylic alcohols by tin–lithium exchange of (E)‐α‐stannylvinyl sulfides

“…Substituted allylic alcohols are usually prepared by the Reformatsky reaction of the corresponding ketones [20], or by a Horner-Wadsworth-Emmons reaction [21,22], but a mixture of isomers is often obtained. Although substantial progress has been made in the synthesis of (E)-di-and (E)-trisubstituted allylic alcohols [23][24][25][26][27], the one-pot synthesis of (E)-2,3-disubstituted allylic alcohols remains a formidable challenge [28].…”

A Facile Stereoselective Synthesis of (2E)‐3‐Silylallylic Alcohols by Hydromagnesiation of 1‐Aryl‐2‐silylacetylenes

“…[2] Although substantial progress has been made in the synthesis of (2E)-di-and (2E)-trisubstituted allylic alcohols, [3][4][5][6][7] the direct synthesis of (2E)-2,3-disubstituted allylic alcohols remains a formidable challenge. [8] The stereocontrolled synthesis of allylic alcohols containing metal or heteroatom functional groups is also of considerable interest in organic synthesis because many useful functional-group transformations can be achieved by introduction and removal of metal or heteroatom functions.…”