CH‐Acidität in α‐Stellung zum N‐Atom in N,N‐dialkylamiden mit sterisch geschützter Carbonylgruppe zur nucleophilen minoalkylierung

Abstract

Sterically protected amides 1 such as the 2,4,6-triisopropyl-benzoic acid derivatives 3, 8b and 10 undergo readily H/Li-exchange with s-butyllithium at the CH3N-or CH2N-groups. The resulting organolithium compounds (cJ: 9, 11) are alkylated and hydroxyalkylated with primary haloalkanes, aldehydes, and ketones under chain elongation in the amine position of the amides. The (EI2)-rotamers of the dialkylamides 7 and 8 are separated by chromatography; the amides 4-6, 12, and 13 formally derived from P-hydroxyamines are obtained in the (Z)-form only. The configurational (E/Z)-assignments follow from NMR. and IR. data. The erythro and threo configuration of the two diastereomeric amides 12a and 12b are tentatively concluded from Eu (fod)3-'H-NMR.-shift experiments. The results strongly suggest that the H/Li-exchange takes place regioselectively at the CH-N group which is in cis-position to the C=O double bond (+14). The methyl 2,4,6-tri (t-buty1)benzoate (18) can also be deprotonated to the lithium acyloxymethanide 19 which is trapped by alkylation with 1-iodooctane (-20). -The steric protection of the carbonyl groups in the products 4-8, 10, 12, 13, and 20 prevents their ready hydrolysis to amines and alcohols, respectively. Therefore, triphenylacetic acid derivatives 21 rather than 2,4,6-triisopropylbenzoic acid

Steric carbonyl protection metalation and cleavage of highly hindered ureas. Preliminary communication

“…In previous papers we have shown that imides [ l ] and amides with sterically protected but electronically effective carbonyl groups such as triphenyl-acetamides (1) [ 2 ] or tris (t-buty1)phenoxy-derivatives (2) [ 3 ] can be metalated at the a-N-CH- position and cleaved to amines under appropriate conditions. We then turned our attention to ureas 3 with bulky substitution at one of the nitrogen atoms.…”

Tritylketone und Tritylenone. Beiträge zur sterisch erzwungenen Michael‐Addition und zur diastereoselektiven Aldol‐Addition

“…I skizzierte C,C-Spaltung erzeugt wurden. Auch reduktive (Na/Naphthalin [5] [47]) C,C-Spaltungen unter Einelektronentransfer und oxidative C,CSpaltungen (von Trianisylketonen mit Persaure [48]) sind beobachtet worden und iiberraschen in Anbetracht der hohen Stabilitit von Tritylradikalen und -kationen nicht. Schliesslich sind auch die Acetessigester-Synthese von Carbonsauren unter Saurespaltung, die Retroaldol-, die retro-Claisen-, die retro-Mannich-und die relro-Mzchael-Reaktion, sowie zahlreiche Fragmentierungen Prozesse, bei denen tetraedrische Zwischenprodukte, wie das in GI.…”

Metallation of Phosphorylated Aliphatic Alcohols to Configurationally Stable α-Oxyalkyllithium Compounds − Use of the Phosphoryl Group as an Activating Group and Electrophile

“…Primary aliphatic alcohols can be deprotonated after transformation into 2,6-disubstituted benzoates [7,8] or carbamates with a shielded carbonyl group as found by Hoppe et al The success of the latter derivatives stems from their highly enantioselective metallation by sBuLi/(Ϫ)-sparteine [3] to α-oxyalkyllithium compounds, which are configurationally stable below Ϫ30°C.…”