Page 283 - Advanced Organic Chemistry Part B - Reactions & Synthesis

O O O 255
RCO 2 – + (PhO) PN 3 RC O P(OPh) 2 + N 3 – SECTION 3.4
2
O O O Interconversion of
Carboxylic Acid
–
RC O P(OPh) 2 + N 3 – RCN + O P(OPh) 2 Derivatives
3
2
O O
RCN + R′NH 2 RCNHR′ + HN 3
3
Another useful reagent for amide formation is compound 1, known as BOP-Cl, 141
which also proceeds by formation of a mixed carboxylic phosphoric anhydride.
O
O
O O N
RCO 2 – + O N P N O RC O P O
Cl N
O O
1 O
O
Another method for converting esters to amides involves aluminum amides, which
can be prepared from trimethylaluminum and the amine. These reagents convert esters
directly to amides at room temperature. 142
O
CO CH 3 (CH 3 2 CNHCH Ph
2
2
) AlNCH Ph
H 2
78%
The driving force for this reaction is the strength of the aluminum-oxygen bond
relative to the aluminum-nitrogen bond. This reaction provides a good way of making
synthetically useful amides of N-methoxy-N-methylamine. 143 Trialkylaminotin and
bis-(hexamethyldisilylamido)tin amides, as well as tetrakis-(dimethylamino)titanium,
show similar reactivity. 144 These reagents can also catalyze exchange reactions between
amines and amides under moderate conditions. 145 For example, whereas exchange of
benzylamine into N-phenylheptanamide occurs very slowly at 90 C in the absence of

catalyst (> months), the conversion is effected in 16 h by Ti N CH
.
3 2 4
O O
5 mol % Ti(NMe )
2 4
CH (CH ) CNHPh + PhCH NH 2 CH (CH ) CNHCH Ph
2 5
2
2 5
3
3
2
90°C, 16 h
99%
141 J. Diago-Mesequer, A. L. Palomo-Coll, J. R. Fernandez-Lizarbe, and A. Zugaza-Bilbao, Synthesis, 547
(1980); R. D. Tung, M. K. Dhaon, and D. H. Rich, J. Org. Chem., 51, 3350 (1986); W. J. Collucci,
R. D. Tung, J. A. Petri, and D. H. Rich, J. Org. Chem., 55, 2895 (1990); J. Jiang, W. R. Li,
R. M. Przeslawski, and M. M. Joullie, Tetrahedron Lett., 34, 6705 (1993).
142 A. Basha, M. Lipton, and S. M. Weinreb, Tetrahedron Lett., 4171 (1977); A. Solladie-Cavallo and
M. Bencheqroun, J. Org. Chem., 57, 5831 (1992).
143
J. I. Levin, E. Turos, and S. M. Weinreb, Synth. Commun., 12, 989 (1982); T. Shimizu, K. Osako, and
T. Nakata, Tetrahedron Lett., 38, 2685 (1997).
144 G. Chandra, T. A. George, and M. F. Lappert, J. Chem. Soc. C, 2565 (1969); W.-B. Wang and
E. J. Roskamp, J. Org. Chem., 57, 6101 (1992); W.-B. Wang, J. A. Restituyo, and E. J. Roskamp,
Tetrahedron Lett., 34, 7217 (1993).
145
S. E. Eldred, D. A. Stone, S. M. Gellman, and S. S. Stahl, J. Am. Chem. Soc., 125, 3423 (2003).