Pt-catalyzed pentannulations of propargylic esters

ORGN 454

BA. Bhanu Prasad, bhanuba@berkeley.edu1, Brian G. Pujanauski, bgpujanauski@berkeley.edu1, and Richmond Sarpong, rsarpong@berkeley.edu2. (1) Department of Chemistry, University of California, berkeley, CA 94720, (2) Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720
Five-membered rings are a common motif in a variety of architecturally complex natural products that possess important biological activity. Two types of Pt-catalyzed pentannulation reactions beginning from propargylic esters have been developed. Both reactions take advantage of a 1,2-acyl shift to arrive at a Pt-carbenoid intermediate. Metallocarbenoids arising from substrates such as 1 undergo an insertion into an aryl or vinyl C-H bond to arrive at the pentannulated product 2 in good yields (61-84%). The key to this reaction is the use of a PtCl2(PPh3)2/PhIO catalyst combination that allows the in situ generation of the Pt-carbenoids. The second reaction takes advantage of an epoxide fragmentation of 3 via a metallocarbenoid intermediate to yield pyran 4. Sequential oxa-6π electrocyclic ring opening of 4 followed by a novel tandem acyl shift/4π electrocyclic ring closure leads to good yields (46-75%) of cyclopentenone products (e.g., 5).

 

Modern Acetylene Chemistry
8:00 PM-10:00 PM, Tuesday, 12 September 2006 Moscone Center -- Hall D, Poster

Sci-Mix
8:00 PM-10:00 PM, Monday, 11 September 2006 Moscone Center -- Hall D, Sci-Mix

Division of Organic Chemistry

The 232nd ACS National Meeting, San Francisco, CA, September 10-14, 2006