ChemInform Abstract: Vinylspiropentane.

Abstract

In the presence of Pd(OAc)2 the cyclopropanation of the allene (II) by diazomethane (III) affords a 27:63 mixture of the 2‐bromoethylspiropentane (IV) and 1‐bromo‐3‐cyclopropylidenepropane.

Palladium-Catalyzed Reactions of Allenes

“…Cyclopropanation of allenes can be efficiently achieved by using diazomethane in the presence of Pd(II) catalysts (Scheme ). − The reaction procedure is superior over others in terms of high regioselectivity in the sense that the addition occurs at the less substituted terminus with the exclusion of double addition products giving rise to the alkylidine cyclopropanes 667 in good yield. 1,2-Cyclononadiene ( 474 ) produces the corresponding monomethylenation product 668 , and in the case of vinylidine cyclopropane 667 [R 1 ,R 2 = −(CH 2 ) 2 −], bicyclopropylidine was postulated to be an intermediate, which rearranges to form ring-opening products…”

Recent Advances in Synthesis of Cyclopropanes

“…Palladium-catalyzed methylene transfer from diazomethane has proved effective for the cyclopropanation of 1-alkenylboronic acid esters 101,102 , allylic alcohols and amines 103 , 1-oxy-1,3-butadienes 103 and allenes 104,105 . Readily accessible iron complex (η 5 −C 5 H 5 ) (CO) 2 FeCH 2 S + Me 2 • BF 4 − 35 undergoes direct reaction with a range of alkenes to give cyclopropanes (equation 67) 106,107 .…”

Synthesis of Methylene- and Alkylidenecyclopropane Derivatives

“…Better results in terms of selectivity have been achieved by reacting diazomethane and allene derivatives in the presence of Pd(II) catalysts. Under these conditions the reactivity could be modulated in order to obtain good yields of ACPs, with only a limited formation of double addition products (Table ). − The addition occurs at the less substituted terminus. Formation of bicyclopropylidene from vinylidenecyclopropane (entry 7) is only postulated as a reactive intermediate complex, which gives ring-opened products under the reaction conditions…”

“…Reactions with catalytic or stoichiometric amounts of strong acids (HCl, 5d,,,249b H 2 SO 4 , 4a, HIO 4 , CF 3 COOH, AcOH, p -TsOH, , PPTS, Me 3 O + BF 4 - , 201a, strongly acidic resins, 297c, silica gel 276b-d ) and bases (NaOH, ,,,, KOH, 298a, LiOH,5d MeONa, t -BuOK, NaH, ,252b,, KH, n -BuLi, , t -BuLi, LDA, LiTMP, K 2 CO 3 , 4a,c, i -Pr 2 NEt, NEt 3 , ,, NH 3 433 ) have been performed. Alkylations of carbonyl and carboxyl functionalities directly linked to the cyclopropane ring or in the side chains can be achieved by the use of Grignard 260b,276e,294b,437,438 or alkyllithium 332,354b,356,418,437,438 reagents.…”