Metalated allylic ethers as homoenolate anion equivalents

Abstract

similar type of extrapolation to hydrazyl itself implies that ,) > aNl2) as has also been concluded from theoretical consideration.1112Kinetic data on the decay of some of these radicals will be reported at a later date.

3‐Triethylsilyloxypentadienyllithium, a Versatile 1,3‐Diene‐ or Vinyl Ketone‐Building Block

“…In this context we reported recently in a preliminary note that the pentadienyl anions of type I present a convenient C,-unit for both the construction and attachment of the functionalized dienes 11 and dienophiles 111 (Scheme 2) [2]. At the outset of our work it was known that metalated unsubstituted ally1 ethers 2 ( R = H) react with electrophiles in the y-as well as in the a-position whereas metalation of the substituted ethers 1 ( R = alkyl) is extremely slow [3] [4] (Scheme 3). In contrast, 3-trialkylsilyloxy-1,4-pentadienes are smoothly deprotonated to form the symmetrical pentadienyllithium derivatives I which may be substituted by a variety of electrophiles.…”

Catalytic Enantioselective Three‐Component Hetero‐[4+2] Cycloaddition/Allylboration Approach to α‐Hydroxyalkyl Pyrans: Scope, Limitations, and Mechanistic Proposal

“…These cycloadditions are further complicated by difficulties in making isomerically pure 2-substituted acyclic enol ethers. The model Z-configured enol ether 17, synthesized according to a literature method, [20] was studied first in the [4 + 2] cycloaddition/allylboration process. The [4 + 2] cycloaddition reaction was indeed more difficult with such a 2-substituted enol ether (Scheme 7).…”

A Route to (2α,3β,4α)-(±)-2-(Hydroxymethyl)-3,4-pyrrolidinediol Based on the α-Silyloxyallylation of a Glycolaldehyde-Derived Nitrone

“…Both enantiomers of 6a, naturally occurring 1,4-dideoxy-1,4-imino--arabinitol (DAB1) isolated from Arachniodes standishii and Angiloca-Scheme 3 lix boutiqueanus and synthetic 1,4-dideoxy-1,4-imino--arabinitol (LAB1), display powerful activity against α-glycosidases [7] . Our retrosynthetic plan, shown in Scheme 2, involves the isoxazolidine 7a as key intermediate, and the α-Typical examples of functionalised allylic metal com-forded disappointing results; the regioselectivity worsened slightly, the yield of 8a did not increase and, using the chiral plexes include 11a (Z ϭ OMe or OTHP, ML n ϭ Li) [8] , 11b (Z ϭ OTMS, ML n ϭ SnBu 3 ) [9] , 11c (Z ϭ OMe, ML n ϭ amine, no evidence of asymmetric induction was obtained [26] . SnBu 3 ) [10] , 11d (Z ϭ OTHP, ML n ϭ SnBu 3 ) [11] , 11e (Z ϭ OBn, ML n ϭ CrCl) [12] , 11f (Z ϭ OMOM, ML n ϭ Subsequent steps involve formation of 8b (TMSCl, imidazole, 96%) and NIS-promoted iodocyclisation (82%) [27] .…”