Construction of α‐phosphonolactams via rhodium (II)‐catalyzed intramolecular C-H insertion reactions
- 1 May 1995
- journal article
- research article
- Published by Wiley in Heteroatom Chemistry
- Vol. 6 (3) , 195-210
- https://doi.org/10.1002/hc.520060304
Abstract
The Rh(II)‐catalyzed intramolecular CH insertion reactions of N,N‐dialkyl‐α‐diazo‐α‐(diethylphosphono)acetamides 2a,f–j in CHCl3 or ClCH2CH2Cl were found to give monocyclic and bicyclic α‐phosphono‐β‐lactams, 3a and 3f–j, in 43–67% yields via regiospecific α‐CH insertion of the N‐alkyl groups. Similar treatment of N‐benzyl‐N‐isopropyl‐α‐diazo‐α‐(diethylphosphono)acetamide (2b) and the corresponding N‐isobutyl‐N‐methylacetamide 2d in ClCH2CH2Cl afforded mixtures of β‐lactams 3b (35%) and and 3b′ (16%), β‐lactam 3d (47%), and γ‐lactam 4d (10%), respectively, each of which is formed by the competitive CH insertion reaction between benzylic and isopropyl α‐CH bonds and between methyl α‐CH and methine β‐CH bonds, respectively. For the formation of β‐lactams, the selectivity in the rhodium‐mediated CH insertion in ClCH2CH2Cl follows the order methyl > methine > benzylic α‐CH bond on N‐substituents. The N,N‐dibutyl‐α‐diazo homologue 2c and Nα[α‐diazo‐α‐(diethylphosphono)acetyl]‐2‐methylindoline (2k) exclusively produced γ‐lactams 4c (67%) and 4k (81%) via insertion into the methylene β‐CH and methyl β‐CH bonds. tert‐Butyl N‐[α‐diazo‐α‐(dibenzylphosphono)acetyl]‐piperidine‐2‐carboxylate (2m) on similar treatment, followed by deprotection of the benzyl ester afforded the 7‐phosphono carbacepham 6 in 32% overall yield. Similar Rh(II)‐catalyzed cyclization of N‐methyl‐N[4‐benzyloxy‐α‐(diethylphosphono)‐phenyl(diethyl‐phosphono)methyl]‐α‐diazo‐acetamide (2n) led to 1‐[4′‐benzylphenyl(diethylphosphono)methyl] ‐3‐(diethyl‐phosphono)azetidin‐2‐one (3n) in 78% yicld. The phosphono group at C‐7 of 3f was converted into the acetylamino group via a four‐step reaction. Application of chiral rhodium(II) carboxylates 12a–c to the insertion reactions of 2b,c produced α‐phosphono‐β‐and γ‐lactams, 3b and 4c, in 6–24% ee and 25–29% ee, respectively.Keywords
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