The bicyclobutylidene to bicyclooctene rearrangement: Formal syntheses of (±)-ceratopicanol and (±)-hirsutene

Carbocycles from donor–acceptor cyclopropanes

“…Over ten year later, Fitjer and co-workers were able to showcase Snider's conditions in the formal synthesis of both (+/-)-ceratopicanol (7) and (+/-)-hirsutene (10) (Scheme 2). 6 Olefins 4 and 8 underwent smooth transformation to the corresponding tricyclic systems 6 and 9 albeit in lower yields due to isolation of regioisomers in the case of 6 and ringopened product in the case of 9. These compounds were easily converted into intermediates that could be advanced to the natural products.…”

Synthesis and rearrangement of [1,1′-bicyclobutyl]-1-ols and spiro[3.4]octan-5-ols: a general access to bicyclo[3.3.0]octenes (hexahydropentalenes)

“…On the contrary, attempted additions of 13 to 1, and of 12a,b to 2-methyl-cyclobutanone (31) 22 failed. However, 10 6 reacted with 31 to give a single dimethylated [1,1 0 -bicyclobutyl]-1-ol, thought to be 32a, 23 and with 2,2-dimethylcyclobutanone (20) to give the trimethylated [1,1 0 -bicyclobutyl]-1-ol 33 (Scheme 5).…”

“…1-Chloro-1,2,2-trimethyl-cyclobutane(22), 5-chloro-2,3-dimethyl-pent-2-ene(24) and 1,4-dichloro-3,4-dimethyl-pentane(27) At K78 8C, hydrogen chloride was bubbled through a solution of 1,1-dimethyl-2-methylene-cyclobutane(21) (6.66 g, 69 mmol) in pentane (2 ml) until GC analysis [column A, 5 min 100 8C, 20 8C/min to 190 8C; 22 as colourless liquid, bp 95-105 8C/180 Torr, which solidified on cooling; mp 27-30 8C. Preparative GC of the remaining material delivered pure samples of 24 and 27 as colourless liquids.…”

Four‐Membered Cycle Formation Challenge: GaCl3‐Promoted Formal [2+2]‐Cycloaddition of Donor–Acceptor Cyclopropanes to Bicyclobutylidene

“…A distinctive feature of this process (unlike other reactions of DAC 1 with alkenes) is that a carbocationic double Wagner–Meerwein dyotropic rearrangement of the bicyclobutyl system into a bicyclo[3.3.0]octane one occurs, which involves two 1,2‐C shifts and expansion of both cyclobutane rings to cyclopentane ones. It should be noted that a few examples of similar rearrangements are known in literature, but they are not related to cycloaddition processes. It cannot be ruled out that conformation factors favoring the cyclization on the malonyl moiety may also play a certain role in the process in question.…”