Table 1.

Synthesis of Cyclobutene Aldehydes 6 from Alkynyl cyclopropanes^a

Entry	Substrate	Productb	Yield
1			85%
2			80%
3			80%
4			73%
5			82%
6			86%

^aConditions: 1) CuTc (10 mol % ), AgOTf (10 mol %), 13c (1 equivalent), rt, 4-8h; 2) alumina oxide;

^bRegioselectivity (>20:1) was determined by ¹H NMR of the crude product.