1 -Alkynyl-cyclobutanols

Alkylidenecyclopentanones Coupling-induced ring expansion of 1-(1-alkynyl)cyclobutanols proceeds in moderate yields. Some of these products are relatively difficult to prepare by other methods. 

Alkylidenecyclopentanomei alkynyl)cyclobutanols proceeds 11 difficult to prepare by other metho... 

The l-(l-alkynyl)cyclobutanol 120 was expanded by Pd-catalyzed reaction with aryl- and alkenyl halides to produce the 2-(2-arylidene)cyclopentanones 123. The reaction can be understood formally by carbopalladation to give 121, and migration of an electron-rich carbon to Pd to form the palladacyclohexanone 122, and the cyclopentanone 123 is obtained by reductive elimination of 122 (see Chapter 3.8.2) [40],... 

Larock and Reddy obtained the 2-alkylidenecyclopentanone 72 by the reaction of l-(l-alkynyl)cyclobutanol 71 with iodobenzene. The bicyclononanone 74 was obtained from 73. Selective formation of 74 demonstrates that the more substituted bond a in the eyelobutanol 73 undergoes exclusive cleavage (or migration) [8,13]. Larock proposed the mechanism of the reaction of 75 involving ring expansion of 76 to form palladacycle 77 and reductive elimination to give 78. 

U.v. irradiation of the unsaturated A-seco-5-ketone (324) gave none of the expected oxetan (325), but instead produced the cyclobutanols (327) as major products, along with a little of the B-seco decarbonylation product (328). Cyclobutanol formation proceeds through hydrogen transfer from C-2 to the carbonyl oxygen, which is followed by cyclization of the 2,5-biradical (326). Similar reactions occur with the alkynyl-ketone (329) and with the saturated analogue (330). ... 

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