Methods of synthesis of cyclobutenediones

Issue in Honor of Prof. S. Swaminathan ARKIVOC 2005 (xi) 48-77 Analogous method for the preparation of highly functionalized cyclobutenediones was developed by Knochel et al.75 based on zinc-copper reagents (Scheme 47). FG-R1 O FG-R1Cu(CN)ZnX Cl O FG-R1 O FG-R1Cu(CN)ZnX excess O FG-R2Cu(CN)ZnX FG-R2 O FG-R1 O Cl unsymmetrical symmetrical 77b 77a FG-R = functionalised alkyl 57-81% 67-89% Scheme 47 5. Synthesis of benzocyclobutenediones As discussed in section 1.2.7, some benzocyclobutenediones were prepared via Diels-Alder addition reactions of some dienes with olefins. Benzocyclobutenediones were also synthesized starting from certain aromatic compounds. Benzocyclobutenedione 78 was first synthesized by Cava et al.76 using simple organic transformations from 1,2-diiodobenzocyclobutene as shown in Scheme 48. I ONO2 O 2Et3N 2AgNO3 I ONO2 O 78 75% Scheme 48 Bromination of 3,8-diphenylnaphtho[b]cyclobutene 79 with NBS generates tetrabromoderivative 80 along with a mixture of other bromides. The tetrabromide 80 reacts with silver trifluoroacetate and water to give 3,8-diphenylnaphtho[b]cyclobutene-1,2-dione 81 (Scheme 49).77 Ph BrPh Ph O AgOCOCF3 NBS Br Br H2O O Br PhPh Ph 81 79 80 41% Scheme 49 Also, 3-aminobenzocyclobutenedione 83 has been prepared via the oxidation of luminol 82 using t-butyl hypochlorite (Scheme 50).78 ISSN 1424-6376 Page 71 ©ARKAT USA, Inc 0