Identify as many reactions as possible in the synthesis below (ex 15 -> 16 grign
ID: 1062042 • Letter: I
Question
Identify as many reactions as possible in the synthesis below
(ex 15 -> 16 grignards reaction [I know its not])
TBSO CuCN CO2Et FeCl3, DMF, 0 to 50 °C. 1. LDA, TMSCI 17 CO2Et COzEt TMSO CO2Et 2. CH212, Et2Zn 46% 88% three steps 16 15 14 TBS 18 (ca. 6.5:1 dr.) conEt 1. TBAF CHO 1. Ph3P CH2, THF. CO2Et N2 22 78 °C (73% LDA, THF, 0 °C 2. TsCI Sr.H 2, DIBAL-H, PhCH 5 H 25-40%, -78 °C (90% 20-30% recovered K2CO3. 81% MeOH 2 steps starting material Tso (78%) 21 19 elative configuration of 18-21 unknown H owe PtCl2 (cat.), nBuLi, MOMCI, THF PhCH., °C (46%, two steps, (91% when isolated, or 56% from 12) generally used crude) Meo" OMe 24 (2:1 Z/E) 23 (4.5:1 dr) 12 "constitutes a formal synthesis 25 (15%) of echinopines A and B PCC, CH2CI2 (23%U (40% OH 26 CO2Me 2: echinopine BExplanation / Answer
15 ----> 14 ; Saegusa type ring expansion
19 ----> 20 ; base mediated ring closure
20 ----> 21 ; wittig reaction followed by ester reduction
21 ----> 23 ; Alkynylation {with the Ohira Bestmann reagent(22)}
23 ----> 12 ; Lithiation and methoxymethylation (with MOMCl)
12 ----> 24 ; Cycloisomerization
24 ----> 2 ; Enol ether oxidation
24 ----> 23 ; Cycloisomerization