Diazo‐Transfer Reaction with Diphenyl Phosphorazidate

Abstract

Diphenyl phosphoraziddte (DPPA) was used as the azide source in a one-pot synthesis of 2,2-disubstituted 3-amino-2H-azirines 1 (Sc/zeme I ) . The reaction with lithium enolates of amides of type 2, bearing two substituents at C(2), proceeded smoothly in THF at 0"; keteniminium azides C and azidoenamines D are likely intermediates. Under analogous reaction conditions, DPPA and amides of type 3 with only one substituent at C(2) gave 2-diazoamides 5 in fair-to-good yield (Scheme 2). The corresponding 2-diazo derivatives 6-8 were formed in low yield by treatment of the lithium enolates of N,N-dimethyl-2-phenylacetamide, methyl 2-phenylacetate, and benzyl phenyl ketone, respectively, with DPPA. Thermolysis of 2-diazo-N-methyl-N-phenylcarboxamides 5a and 5b yielded 3-substituted 1,3-dihydro-N-methyl-2H-indol-2-ones 9a and 9b, respectively (Scheme 3). The diazo compounds 5 8 reacted with 1,3-thiazole-5 (4H)-thiones 10 and thiobenzophenone (13) to give 6-oxa-1,9-dithia-3-azaspiro[4.4]nona-2,7-dienes 11 (Scheme 4 ) and thiirane-2-cdrboxylic acid derivatives 14 (Scheme 5 ), respectively. In analogy to previously described reactions, a mechanism via 1,3-dipolar cycloaddition, leading to 2,5-dihydro-l,3,4-thiadiazoles, and elimination of N2 to give the 'thiocarbonyl ylides' of type H or K is proposed. These dipolar intermediates with a conjugated C=O group then undergo either a 1,S-dipolar electrocyclization to give spiroheterocycles 11 or a 1,3-dipolar electrocyclization to thiiranes 14.

Synthetic Exploration of α‐Diazo γ‐Butyrolactams

“…Deacetylative diazo transfer reaction has been described for α-oxalylated cyclic ketones [15] and for lactams, ethyl oxalylation protocol has also been described in the literature. [16] Oxalylation is a markedly cheaper alternative to the traditionally employed trifluoroacetlation [17,18] or to diazo transfer onto nonacylated monocarbonyl substrates which requires the use of strong bases such LDA [19,20] or NaHMDS. [21] To our delight, αoxalylation of lactams 1 worked rather well according to the literature protocol [17] and delivered target α-oxalyl derivatives 2 in generally good yields (Scheme 2).…”

Transition-Metal-Free Fluoroarylation of Diazoacetamides: A Complementary Approach to 3-Fluorooxindoles

“…The reaction was quenched with saturated NaHCO 3 solution (30.0 mL), and the aqueous phase was extracted with ethyl acetate (20.0 mL×3). The combined organic phase was dried with anhydrous Na 2 SO 4 , the crude product was purified by column chromatography on silica gel (petroleum ether : ethyl acetate = 10:1 to 2:1) to give the pure diazoacetamides 1.Diazoacetamides 1s, 21 1t 22 and 1u23 were prepared according to the reported references, and the characteristic data are consistent with the reported references.General Procedure for the Synthesis of 2. To a 10-mL oven-dried vial with a magnetic stirring bar, NaOAc(24.6 mg, 0.3 mmol), NFSI (94.6 mg, 0.3 mol) andanhydrous DCE (1.0 mL), diazoacetamides 1 (0.2 mmol) in anhydrous DCE (1.0 mL) was added to the mixture under argon at 80 o C over 30 min via a syringe pump.…”

Revisiting Keteniminium Salts: More than the Nitrogen Analogs of Ketenes

“…[50] The depolymerization of naturally abundant biomass macromolecular resources is an exciting area of research in the field of sustainable chemistry. Synthesis of 3-arylamino-2-chloroindoles through keteniminium salts.…”