CHELATE-STABILIZED 1,3-BIS(ACYLOXY)-1,3-D IETHYLDIBOROXANES FROM TRIETHYLBOROXIN AND CARBOYXLIC ACID ANHYDRIDES

Triethylboroxin (A) reacts with carboxylic acid anhydrides (RCO)2O [R = Me: 1a; Et: 1b; tBu: 1d; Ph: 1e] with various rates to give high yie lds of the 3,7-dialkyl-1,5-diethyl-4,8,9-trioxa-2, dioxonia-1,5-dibora tabicyclo[3.3.1]nona-2,6-dienes OB(Et)OC(R)OB(Et)OC(R)O (2) [R = Me: 2 a (X-ray crystal structure analysis); Et: 2b; tBu: 2d; Ph: 2e], presum ably via the unstable compounds OB(Et)OB(Et)OC(R)OB(Et)OC(R)O (3a, b, d, e). Compound 1c (R = CF3) reacts with A to form mixture of 1,3-diet hyl-1,3-bis(trifluoroacetoxy)diboroxane O=C(CF3)OB(Et)OB(Et)O(CF3)C=O (2c') and 2c (R = CF3) at room temperature. Whereas two compounds of t he type 2 do not comproportionate, 1a-e spontaneously form the mixed s ubstituted carboxylic acid anhydrides lab etc. on mixing at room tempe rature (GC, C-13 NMR). From the O-17 enriched A and 1a-e the O-17-enr iched compounds 2a-e* with BO*B and [GRAPHICS] BO*OCR groups are obta ined. A exchanges O atoms up to 200-degrees-C with succinic anhydride (1f) forming 1f or with phthalic acid anhydride (1g) forming 1g* and 3g. The mixed carboxylic acid anhydrides 1xy are cleaved, and the mi xtures of 1 are separated with A to yield the uniform 3,7-dialkyl-subs tituted compounds 2.